rear backing plates

[Chevy nutcase]

On the 71 c10 rear I am rebuilding for my 66 c10 I'm in need of the backing plates and after a bit of searching I can't seem to locate anyone selling them new. what I did find was a guy on marketplace with a healthy collection of these trucks from 60-72. I have him looking for a good set from a 71 or 72 and my question is, would c10 trucks from 64-72 all be the same backing plates if they have the gm 12 bolt with 11" brakes? I need all the other pieces as well like the ebrake lever, self-adjuster arm, etc. and I may as well take those if in useable condition and are compatible