Ring gears are easy to change if you have an oxy-acetylene torch, but...the flywheel has to be out of the truck. Just heat it evenly and they are easily pushed off. Heat the new one and it will push on. I think the flywheels are the same in these trucks up to 1955 but if you can count the number of teeth on your flywheel (if they are not rusted away) just make sure you buy one with the same number of teeth. I think they have 139 teeth but a little research should help you determine what you need. It sounds like you are making a lot of progress on your truck.
Good luck.