[68WarDog]

Did the 73 Grand Prix SJ 455 car come with an 8.2, 8.5 or 12 bolt rear end? Also what U joints? And do the rear end differs from the chevy?

[fireprix]

I’d guess it either has the 8.5” 10 bolt or it may have the MP78 Pontiac rear. If the cover has 2 half moon cutouts and a drain plug, it’s the MP78 which is a 12 bolt carrier with a 10 bolt cover. It’s a strong rear but aftermarket support is 0. Another way to tell is drum size. 9 1/2” drum is 8.5” 10 bolt. 11” drums is probably the MP78. Not sure on U joints. I’ve owned 2 different 75 GP both LJ with a 400. Each had a different rear.