This winter, take a winter vacation to the sunny, warm, rust free southwest, like Arizona. Bring your truck and a trailer. Start watching Craigslist now in Phoenix and the surrounding area for a truck like yours with a blown engine or trans, or very high miles. Bodies are usually nice but the paint might be a bit burnt. Buy something decent and take it home and take everything good off you truck and transfer it to the new truck. Engine, trans, differentials, interior, anything you want to keep. That way you can utilize every rust free part from the Arizona truck and I guarantee it will be easier than swapping only the frame on your old truck. When you're done, part out whats left. As a guy who lived in the rust belt for over 50 years, I am always amazed at how rust free stuff is down here!