Early 7.25 backing plates will not fit the 8.75 ends, even if you knock out the stud...different size pocket. The 73-up 7.25 plates are interchangeable though. You could simply drill the SBP into the later drums, but the problem you're going to have is the register on the axle flange. The Drum would only be centered by the studs and that's not a good plan at all.