1964 Dodge Dart - Wheel Stuck

I have a 1964 Dodge Dart and the left rear drum is stuck. We removed the wheel/tire last night and tried to get the drum to move but no luck. We used PBblaster and thumped around the outside edges of the drum. Rust came out, but still no luck in moving it. How does the drum come off anyway? There isn't a castle nut to be removed, so how is it held in place? Thanks