It doesn’t matter.
We know he has BBP axles. You can clearly see in the picture that those are SBP drums that had the lug holes hogged out to fit on the BBP axles, same for the center register.The OP even told us that’s exactly what he did.
So, we’ve already got mismatched parts. Are the backing plates SBP or BBP? I honestly don’t know, which is why I told him to measure them. The space showing past the drum in the picture is meaningless with the info we have now.
No mismatch of SBP and BBP parts is going to work properly. Anyone that takes a lathe to drums to make some random, unknown mismatch of brake parts fit together instead of buying/finding the right parts is an idiot. The right parts will fit without modification, they’re not hard to find or terribly expensive, and they’re the most important piece of safety equipment on the car.
