it would depend on which rearend you're going too. Assuming the 70 has a 7.25 and that the 73 has a the 8.25, then you'd be fine. But if either of those two cars were to have the 8.75, you could run into issues. to my knowledge, there were two u joint sizes used in A bodies, a small yoke and a large yoke. the 8.25 and 7.25 both use the same small yoke u joint. The 8.75 used both sizes depending on which yoke and carrier.