Squarebody LS Swap Guide | 73-87 K10 Parts List
Squarebody Chevy trucks, also known as the C/K10 series, built from 1973 through 1987 (through 1991 for SUV bodies) are incredibly popular, and for good reason. These trucks are not only good looking, but also durable, easy to work on, and affordable. They also lend themselves to LS swaps quite well. There are some major differences in the C-series (2WD) and K-series (4WD), which require different parts to swap Chevrolet’s most swapped engine into the K-series chassis. K10 LS swap parts are harder to find, so we have put together this guide for LS-swapping a square body 4x4 K10 truck.
Squarebody LS Swap Considerations
Before we get into the details, LS swaps often require installing the engine and removing it several times to get things exactly right. Instead of fighting a heavy engine, you can use our LS engine mockup block to get the dimensions and positions dialed in before you drop in the actual engine. This bolt-together steel mock-up block works as a stand-in for all LS-series engines, and can even be used as a test block for heads, transmission, accessories, etc. Check out our guide on How To Replicate LS Engine Dimensions for tips on using our Solo Swap mock-up block and LS swap mockup heads.
Square Body LS Swap Motor Mounts & Driveline Position
The chief difference in C and K series squarebody trucks is the front drive axle. Unlike the later K1500 chassis with uses an unsprung IFS front drive, the ’73-’87 squarebody chassis uses a leaf spring-mounted solid axle in the front. This means that the front axle moves with the suspension, requiring some special consideration in terms of engine mounts and oil pans. If the axle housing hits the engine, it is pretty much game over for that engine. Not to worry, as Speedway Motors is here to help with your 4x4 square body LS swap.
K10 LS Swap Transmission and Transfer Case Options
For any pre-1988 Chevy 4x4 (1992 for SUVs), you need to reuse the original transfer case. This is due to a change on which side the front driveshaft exits the transfer case. Before 1988 (or 1992 for SUVs), the front driveshaft is on the passenger side of the engine, this changed when GM went to the IFS front axle design. For the swapper, this means that the late-model transfer cases are not usable unless you change the axle. This can be addressed in several ways.
Using the original transmission in your k10 LS swap in most cases means using a TH350, TH400, or 700R4 overdrive automatic, is certainly an option for a K10 swap. This eliminates dealing with adapting the transfer case to another transmission. The drawbacks are that you don’t get modern automatic transmission performance. The TH350 and TH400 are relatively power hungry, they soak up a decent amount of horsepower to operate, when a modern 4L60/5 or 4L80 are more efficient units.
Adapting an older GM transmission to an LS is easy. You just need a LS swap flexplate adapter and our torque converter adapter ring for the torque converter snout that rides inside the end of the crankshaft. Speedway Motors’ adapter flexplate and torque converter sleeve are the perfect choice for an LS swap into a square body 4x4 to get the job done. By using the original transmission, you save a lot of money, and it simplifies the drivelines, as you can reuse the original shafts with the right motor mounts.
The other option is adapting a late model 4LXX transmission to your existing transfer case. This is an expensive proposition, as the kits for this cost $750-$900 and require removing the original tailshaft and housing from the transmission. For a modern GM transmission swap, Speedway Motors offers a 4l80E swap mock-up transmission to test fit sensors, transmission pan clearance, and mounts. Check out our guide on LS manual transmission options for more resources on selecting the best LS transmission for your squarebody Chevy.
For our K10 LS Swap Kit, we are keeping the original (or a period-correct) transmission in the lineup to simplify the process. We are opting for the Holley Hooker BlackHeart LS swap mounts, which feature a dual-position mounting. The forward position is for swaps using a 6L80/90 transmission adapted to the stock transfer case, keeping the transfer case position stock, so that you can reuse the driveshafts. If you use the forward position, the front engine crossmember must be notched to clear the oil pan. The rearward position is for swaps that are using the original transmission, again allowing the use of the original driveshafts. These mounts work with the factory GM truck oil pan, or our low profile LS swap pan and use the original clamshell style frame mounts.
This is the most affordable option for the typical LS swap into a K-series Squarebody truck, and the simplest option. If you need a new driveshaft, Speedway Motors has you covered. Check out our selection of Squarebody LS Swap Driveshafts, yokes, and accessories to get your driveline hooked up.
Best Squarebody LS Swap Headers & Exhaust
When it comes to exhaust, headers are considered the best, but the factory manifolds are not bad at all. In fact, a stock LS engine will perform quite well with the factory manifolds, and the truck manifolds fit the K10 chassis. If you want to upgrade, there are many options. Our Squarebody LS Swap Headers & Exhaust can be tailored to your specific vehicle so you only get the parts that fit. The best option for a K10 LS swap is a set of shorty headers, such as Flowtech’s shorty LS swap headers . These clear the motor mounts and come with O2 sensor adapters for those that are retaining the stock EFI or going with an aftermarket EFI solution.
The rest of the Chevy K10 LS swap exhaust can be pieced together or bought as a kit. For our recipe, we selected the Speedway mandrel bent 2.5 exhaust tubing kit, which will provide everything you will need to build a complete dual exhaust from the manifolds or headers back to a rear exit setup.
Squarebody LS Swap Radiator & Cooling System
If your truck is a factory V8 build, then the original radiator is suitable for an LS swap, as the LS doesn’t need extra cooling over the original SBC engines. Simply add our LS steam port hose adapter and you’re good to go. If you want to upgrade, you have many options for radiators. This radiator for truck applications is a 2-row aluminum radiator that fits the 1972-87 Chevy K10 truck and features a transmission cooler and a steam vent port for the simplicity. For a better picture on selecting your K10 LS swap radiator check out our Toolbox guide on how to choose a radiator for your car.
Squarebody LS Swap Fuel System & Delivery
Regardless of the year of your K10 truck, the stock fuel pump will not work with an LS engine. For all but 1987 (up to 1991 for SUVs), the fuel pump was a mechanical unit mounted to the original engine. However, in 1987, GM switched to EFI, which requires an electric fuel pump. The fuel pump on an ’87-’91 is not powerful enough to feed an LS. An LS engine requires 60 psi of fuel pressure with a return line going back to the fuel tank. Some LS engines have pressure regulators at the fuel rail, while others have separate regulators. You will also need an EFI fuel filter between the tank and the engine to ensure your fuel is clean. In most cases, it is easier to mount a combination LS fuel regulator and filter under the body near the fuel tank. This shortens the return line distance, saving you time and money and keeps the engine bay cleaner without having to mount a regulator on the fender apron.
The fuel pump itself can be frame rail mounted or in the tank. The best option is an in-tank pump, as they run cooler and have fewer issues with placement and don’t require gravity feed from the fuel tank. In-tank fuel modules, such as the Aeromotive Phantom 340, are quite easy to install and work quite well. You can also modify the original fuel sending unit in the fuel tank to carry an in-tank pump. For our install, we selected the Aeromotive Phantom EFI Engine Swap Fuel Pump kit.
You will need a selection of fittings and adapters to install the fuel system. Most LS swaps use AN -6 (3/8-inch) automotive fuel line and fittings. See our squarebody LS swap fuel system & delivery options for the best solutions for your specific build needs.
Squarebody LS Swap Wiring Harness & ECM
There are many options for the engine controller and harness. What you will need depends on the engine you are going to use. The early LS engines used a 24x reluctor wheel (black sensor) on the crankshaft from 1997 through 2006, and a 58x wheel (gray sensor) in 2006 and up engines. The harness and ECM must match this, or the engine will not run. This is not something you can change easily, so don’t expect to be able to change the parts. The sensor is at the rear of the passenger side of the engine block.
Speedway Motors offers a wide range of squarebody LS Swap wiring harness & ECM components for your engine, you just need to know what year and model the engine is. We opted for an OEM LM7 Vortec harness for our build. This uses the original ECM that came with the engine itself. You will need the original ECM for the engine (year and engine RPO). It is not always feasible to pair any LS engine with any other LS ECM; they must match for the ECM to read and control the engine.
If you don't have the OEM ECM or don’t want to use it, you can always go with a Holley Terminator LS controller. These come in several flavors with options such as drive by cable or wire, and built-in transmission control. For our build recipe, we selected a Holley Terminator X Max 550-917 with built-in trans control and drive-by cable operation.
Squarebody K10 LS Swap AC Compressor & Accessories
GM LS engines came with a wide variety of accessory drives, some of which fit the K10 chassis. Unfortunately, the most common accessory drive, the Vortec truck drive, does not clear the frame rails when used with the AC compressor. Any LS accessory drive that uses the low-mount AC compressor hits the chassis. The best fitting factory drives are the C5 Corvette and 4th Gen F-body Camaro/Firebird (‘98 and up LS1), however depending on the motor mounts, you still may need to notch the engine crossmember to clear the AC compressor. If you are not running AC, then this eliminates most of the fitment issues.
Aftermarket LS swap accessory drive kits are available to clean up the look of the engine and provide better chassis clearance. For our recipe, we selected the Holley mid-mount complete drive kit, which comes with everything needed to install a complete accessory drive, including a new Sanded S7 AC compressor, 150-amp alternator, water pump, and crank pulley. This is the master accessory drive kit; you can buy smaller kits if you don’t need all the components themselves.
Squarebody LS Swap Resources, Tools, and Equipment
Speedway has quite a few resources for you to learn from, like a comprehensive LS swap how-to guide, a best LS engine identification guide, and of course our extremely popular 5.3 LS engine build recipes, and 6.0 LS engine build recipes guides with multiple build lists by desired horsepower level.
Need even more information? Learn how-to swap an LS engine into almost anything with the help of CarTech Books available right here at Speedway Motors.
’73-’87 K10 LS Swap Parts List
Explore our '73-'87 4x4 LS swap kit to find our shopping list of parts required to swap an LS engine into your squarebody Chevy K10 truck. This is not every piece needed, but this covers the essentials to make your swap a success. Each vehicle and engine will require specific parts for their unique application. This is simply a guide to help you find what you need for your truck’s LS swap.
