The bolt pattern on the backing plate doesn't matter at all, the offset is the problem. BBP 7.25" backing plates only have 4 bolts, they work fine on BBP 8 3/4's if you drill the 5th hole and are identical otherwise.
The SBP 7.25 and 8 3/4 drums and hardware are the same, the backing plates ARE NOT. The offset on the axle flange is different between the two axles, and therefore the offset on the backing plates is different. The only backing plates that can be used on SBP 8 3/4 axles are SBP 8 3/4 backing plates. Same for SBP 7.25 axles, they can only use backing plates from a SBP 7.25.
