Difference in drum brakes A-B Body

The axle length would be different because the standoff, from the bearing retainer to wheel mount surface, is about .25" shorter on an a body 8.75 vs the BBP B body axles.

That's why when you put the BBP A body aftermarket axles in an A rear, the track increase by about 1/2".

A body 8.75 brakes are their own animal. They don't play nice with any of the BBP axles/brakes.

The only way to use A body 8.75 brakes is if you special order a set of axles using the A body standoff distance. You also need to have the center turned to accept the redrilled A drum smaller center registe , or open the hole in the drum to BBP size.