Rear Brake Identification

I just picked up a '73 CJ5 that one of the previous owners stripped all...and i mean all of the rear brake hardware off with the only exception being the backing plates. How do I tell if these are 11" or 10" drums that I need to rebuild?

Additionally, the front axle was swapped with a 78 Dana 30 with disc brakes.

 

Should be 11 inch on a 73 measure across the backing plate where the drum would ride should give some idea

 

Yes, a '73 should have the 11'x2" Bendix brakes from the factory. Look at the TSM here http://oljeep.com/gw/74_tsm/9-BrakesWheels.pdf at figs. 9-22 and 9-23. The diameter of the brakes is from shoe surface to opposite shoe surface. You can see where the shoes would ride on the backing plates. Loking at the backing plates, there will be little plateaus where the steel backing of the shoes rides; the shoe material is about 1/4" out beyond those.

It will be difficult to find some of the pieces you will need to put these back together. There's no current aftermarket source for the parking brake strut and lever, and maybe the shoe guide plate. They would be reused, since they don't wear out.