7.25 Brake Backing Plate Interchange
The number of bolts for the backing plate isn’t really that big of an issue. The backing plate offset is though. If you’ve got the 5x4” small bolt pattern axles then you have to use 10” backing plates from a small bolt pattern 7.25 rear axle. That’s about it. So your only donors are A-body’s with a small bolt pattern 7.25” and 10” brakes. The later large bolt pattern 7.25” stuff does not interchange with the small bolt pattern 7.25’s.