My preference is to stick with the original size/style unless you have a specific reason to switch. I'm not sure of the change points offhand, but I think your car should have the brakes without the hold down "nails", which I think means the slot in the piston is important.
The factory went down on bore size later on (and finally to 9" brakes), supposedly because in some cases the rear brakes are too strong and can lock up before the fronts. So far at least, I've not found that to be a problem with my own cars. But obviously it can depend on what pad & shoe compounds you use, how hot they are and so on. I got one set of replacement pads that were so bad I took them back off and threw them away!
BTW, the books don't seem to mention this, but those shoe support posts are adjustable. If they are badly worn, you can get a mysterious "clunk" when releasing the brake pedal after a stop. Adjusting the pins to hold the pads parallel to the drum solved the clunk.