A body BBP axle length for 8 3/4"

All these guys telling you there is no such thing as a OEM a-body 8 3/4 bbp axle, are right.
There are bbp 8 3/4 a-body axles but they are aftermarket, and usually require b-body brakes, drums, and backing plates. The offset from the wheel mounting flange to the backing plate is different on an a-body 8 3/4 from all other 8 3/4s because of the small thin brake shoes.