The easiest brake upgrade 8 3/4

The SBP axles had a different offset than the BBP axles. The backing plates have an offset to match the axle offset. So if you use SBP axles (even redrilled) you have to use SBP backing plates. You will have to find a set of SBP drums and redrill them to BBP and use them with the correct offset SBP backing plate. If you DON'T, the back of the drums will drag on the backing plates.

IF you use aftermarket or cut down B/C/E axles, they have the correct offset to use the BBP backing plates from other models (including the 73 BBP backing plates).

It's confusing, but just remember to match the backing plates with the axles you are using.