It depends on which car the rear end was in, my 1966 Dodge Coronet Deluxe 6 cylinder 3 speed stick car had 10x2 inch on that 7 1/4, my 1969 Dart GTS came with 10.0x1 3/4 on the 8 3/4 and I'm sure that the slant six A body cars came with 9.0x?? shoes and drums on them
BBP 7-1/4 used 10X2-1/2 on every one that I have had. The assemblies will bolt right on an 8-1/4 and 8-3/4. Using them on an 8-3/4 you need axles with the right bearing spacing for them.