Strange situation on rear brakes - 67 Barracuda

11"x2.5" was a standard Police Special Option rear drum and shoe size in the early and mid 60's, at least for B-bodies. So that is a possiblitly that needs to be explored.

What the OP needs to do next is to remove one or both of the shoes and lay them inside the drum and see if the arc of the shoe is very close to the arc of the drum. It will be obvious at that point if these are 11" shoes or 10" shoes; 11" shoes would lay in like a glove. They do look like 10" shoes but this does need to checked to understand the set-up better. A pix of the shoes in the drum would be good to see.

It looks pretty certain that the backing plates are for 10" from the original set of pix.