upgrading from 2″ rear brakes to 3″

Greetings. Some of you may remember my saga with the damaged axle shafts for my 73' Polara. It appears that I have found someone with a 71' Fury Suburban that is willing to sell me a set. During the exchange of e-mails, it occurred to me that wagons typically came with either 2 1/2"-3" rear brakes. I asked if he would be willing to sell the backing plates along with the axle shafts. Aside from the obvious shoes and drums, what else besides the backing plates would need to be changed to upgrade the size of my rear brakes?