Does anyone know how to tell if a 10 inch brake backing plate is for an A body or a B body when you don`t know what car they came from. I want to use then on an 8 3/4 housing. The brakes that are on them measure 2 1/2 wide but I`m not sure if they are the original brakes or not. I want to have axles made with the 4 1/2 bolt pattern and need to know what drums to buy. Thanks for any help.