Brake size

Yeah, the overall outer size of the drum, as given by Rock Auto, is completely irrelevant. The key measurements are the inside diameter of the drum (machined surface), and the width of the friction material on the brake shoe (the machined surface on the inside of the drum will be slightly wider). 10 x 1-3/4 would be an A-body rear drum for a V8 car or disc brake car.

You should not have wider shoes in the back than in the front — that doesn't make sense.