I'd look for a better one. If your frame is real bad in the back then I could imagine that the rest isn't so good eather. So it wouldn't be worth your time to try and patch it. Do you have any pics on what it looks like? It would be easier to say what I think if I could see it. And for the small truck frame idea if never heard of someone doing that. Although I have heard of people swapping different model jeep frames before.