Since the last A body Cuda was built in '69, it couldn't have factory "bell" drums that were only offered beginning in the '70 model year...
Factory 10 inch brakes on a 7 1/4 rear weren't totally uncommon, just optional. Had them on my '66 wagon, '68 GT and a '73 Dart 4 dr. Ordering front disc brakes would also automatically get you 10" rear drums, regardless of rear end size.