Nope not the same
I got lucky and scored an 8 1/4" axle for $50.
Had just had the brakes redone I'll be using the backing plates,drums,hardware and shock plates.
Mine was from a satelitte , some of the B/C-body axles can still be had for pretty cheap...
I think the big difference in A-body brakes is due to the offset of the axle flange some have adapted them but there's some machining involved.
And I think the end result would be a questionable braking system.
see bigblockdart.com or moparts.com(all you ever wanted to know about the chrysler 8&3/4" axle) tech archives they have some really good detailed charts on the differences in axle dimensions...
Joe