8 1/4 vs 8 3/4???

Dartnut said
They didn't build 8 1/4 sbp rear diffs, so you have only one choice and that's to go with the 8 3/4. The 8 3/4 is stronger and also a lot more expensive to buy. Good luck.

They did have small bolt pattern available with 8.25 in '73 and up cars, a car could still get small bolt pattern if it had drums all the way around.