All A-body rear axle assemblies with bolt into any A-body. They all are around the same width and have a 43" spring to spring measurement. The differences between 7 1/4, 8 1/4, and 8 3/4 will require some other changes when swapping. To go from a 7 1/4 to an 8 3/4 requires changing the U-bolts and shock plates, and to shorten the driveshaft. Depending on which wheels are used, sometimes the wheels have to be changed too. The '64 and earlier 13" wheels will likely not bolt down flush with the 10" drums due to the wide wheel slots. The 14" wheels are not a problem. Other combos may require several other mods/changes as well. As an assembly, The 8 3/4 A-body rears were pretty much identical from '66-72, except for the flared drums that started in 1970. The 3rd member housing casting numbers, and u-joint sizes varied depending on application, but, those are minor and easily adapted if needed or desired.
