7&1/4 vs 8&3/4 OAL. both BBP

The info you need is right here:
An accurate 8 3/4" rear axle width list
Drum to drum, the A body BBP 7.25 is 56 3/4", the A body BBP 8.75 is 57 13/16" (about an inch wider overall, or about 1/2" each side).