Jeff, Nice lookin truck. Your doors will interchange with a chevy. They are pretty rusty but I've seen worse so repairs are possible.
Just so you know almost all of the cab and body parts are interchangeable with the Chevy. The GMCs have a different filler pannel between the front fender and the grill, because of the difference in the grill for the chevy. Every other body part that I know of should fit with no problem.
It looks like you have a fun project ahead of you. Good luck and enjoy the trip.
George