7 1/4" rear use 10"x 1.75" brake shoes.
8 3/4" rear use 10"x 2.25" brake shoes.
I don't have a 8 3/4" to compare, but the 7 1/4" drums I have do not have an extra 1/2" of surface/width on them?
All rears use 10" x 1.75 on the small bolt pattern with the 8.75 also. Fronts use 10" x 2.25. That is why you have to get different backing plates when you upgrade to bbp.
