Does anyone know if you can put 2 1/2 brakes on 2 1/4 backing plates using the 2 1/2 brake drum? Roughly measuring, the back depth is the same as the 10 1/2 backing plate. I'm thinking I can buy the hardware kit for the 2 1/2 shoes and the length of the axle stickout will make up the difference. I think the backing plates are off a 66 Coronet? I'm putting them on a 74 Charger. Anybody have any experience with this? Thanks.

Never heard of 2 1/4 backing plates.
Either the shoes were 2" 2 1/2" or 3" for 11 inch brakes.
Drums & backing plates are used together, for whichever shoe size.