11 inch drum brake ID

[miller]

Do you happen to know the part number for that back plate?

Sorry, I don't. Easy enough to measure parts, to figure out what you have. The application (police/taxi) helps, when looking for 3" wide rear brakes.
For my 64 Ply, doing complete conversions, that included a later 8 3/4" rear. Just the way it went, trans and complete rear came off a 67 Coronet R/T. Old brake drums were police 11 by 3, sounded good to me. Drums/shoes bought new, would you believe it, from Pep Boys (groan). That was several years ago.

 

[miller]

Like Fran says, easiest to measure the width, inside the drum itself, if you have the old drums. From there, with the backing plate in place, on the axle housing, axles themselves in place, mount the drum. There's a 'lip' on the drums, that get close to the backing plate lip recess, to keep crap out. Has clearance from the backing plate, and the drum fits against the axle flange.

Part numbers should fall into a year range, that they are good for, but you need to know what year. Only parts book I have is 64, so no go. Or, do a search on that part # you have.