I think it isn't even worth talking about until you get under your new truck and look at the extent of the damage. You might be suprised that it is not so bad.

Looking rusty is a pretty vague way to describe it. Power wash it and take a hammer and hit it on little sections on joints and welds.

I would just hate to see you start an undertaking like that for little gain. It would be a very involved project. Not to mention slight differences if you have different type transmissions.

Your truck is based on the VIN of your frame. At least in MASS it is. That's why you can build a sandrail out of a VW Bug chassis with no body and fiberglass fenders and call it a VW bug.

Depending on the hassle of getting a reconstructed title, you should also weigh that in when you make up your mind.