71 Dart, buying brakes, ugh

Yep, the size is the inside diameter of the drum. Measure the width of the braking surface of the drum before you switch shoes. A 2 inch wide shoe will fit and work in a 2 1/2 inch drum. It's your call on switching or not, all you're giving up is 1/2" of shoe width. I'm greedy when it comes to that, I want all I can get. Don't you just love cleaning up a previous owner's mess?