I agree with you that a frame swap would be the easiest way to go. Converting the original frame to 4WD is always way more work in the long run, and when you need to get parts for it in the future, it's hard to get parts when everything is different.
Well, that depends. The NAPCO's were just converted 2wd frames. You could mount late model axles to the springs, shorten the front axle to fit within the fenders. Add a power steering kit and there you go. May have to fuss with the cross members depending on powertrain choice.
Seems like trying to fit the body to a different frame would be a pain.
