backing plates 9"

Hate to be the one to break this to you, but the only brakes MaMopar ever put on an A body 8 3/4" rear were 10" X 1 3/4". Those are the ones you will have to find if you want to keep your SBP. 7 1/4" brakes won't work on an 8 3/4" rear since they are set up to use a 2 1/2" axle tube end and the 8 3/4" end is 3". Have seen a bunch of 10" SBP brake setups listed here for sale lately. The drums are getting a little hard to find for these brakes but they are still available new. Hope this helps.