Night and day better than Dorman castings!
I'm typically a fan of Dorman products, but after receiving THREE different 674-503 (RH) castings with thin/porous inner collector stud flanges [ordered thru FLAPS, shipped directly from manufacturer] for an early L-76 clone build, I decided to try Speedway's version, which, I assumed was also a Dorman part (though hopefully from an earlier, higher quality batch), however they keep stock on hand, and I happen to live close enough to inspect items in person before purchasing.
Speedway's product was superior in every way! So much so, in fact, that when I brought it home and compared it to the "good" Dorman 674-504 (LH) casting, I immediately purchased Speedway's LH casting, which, naturally, was just as nice.
See photos for comparison of Speedway (spot-faced holes, smoother) and Dorman (drilled-only holes, rougher) castings.
Note- if you need a unit with a choke stove tube, the Speedway RH does not have one; Dorman RH does.