Strange situation on rear brakes - 67 Barracuda

With the drums a hitting the backing paltes where they are, the backing plates are obvoiusly 11" too. OP, have you take a shoe off and set it inside the drum to see if the shoe very closely fits the drums? Yous should do that ASAP before going any further with axles, etc.; please give u a pic of the shoe in the drum, set up against the friction surface. The park brake might possibly work with a mix of 10" shoes and 11" drums.