rear brake swap question

the center register on sbp drums is smaller than lbp drums. they are not interchangeable because of that. the register needs to fit the axle correctly.

I have swapped complete rear brake assemblies from 7-1/4's to 8-1/4's and 8-3/4's (ALL lbp assemblies) worst case I have run into is you have to drill one hole in the backing plate for the fifth mounting stud.