swapping rear question again

[sgtjed]

i have a 70 chev 1/2 ton i am putting in a 71 1/2 ton rear into.
the problem i am having is the u-joint. the 70 rear has u-bolts that hold the drive shaft to the rear and he 71 i am going to has bolts and straps.
the 71 rear u-joint yoke is wider than the one i have in the truck now.
went to autozone and got a conversion u-joint that is wider on one side than the other.
well it would fit perfect cept for the cups are bigger than the yolk on the 71 rear.
the parts guy said both rears take the same u-joint but if used it the driveshaft wont center right since the yolk is wider.
anyone else have this peoblem?
the truck i got thois rear out of had a olds motor init,was supose to be a 402 bb but had been changed out,i am just wondering if they changed the yolk on the rear as well.