I was wondering about this in a different way - I’ve got a set of 65 7.25 10 in backing plates complete with new brakes and e brake cable that I was wondering if the 5th hole was drilled, could they then be used in a SBP 8.75?
I doubt it. The 7.25 uses a 2.5" axle tube. The 8.75 uses a 3" tube. However, in 1982 They increased the tube size to 3" when they changed from tapered bearings to roller bearings with c-clips. The center section is the same and the tubes neck down to 2.5" to fit. Actually those probably wouldn't work either. You still have flange thickness difference to deal with. These later brakes are probably the same as the 8.25" brakes.
