If you want originality, I would go with a 48-55 frame. There is hardly any similarity between 49 and 57 frames. It would be doable but it would be a lot of work to accomplish really nothing. I was cleaning up here a while back and gave several parts pickups away that had good frames. Also, a GMC and a Chev 1/2 ton frame are different. Get one that is a bolt together and save a lot of work even if you have to buy a parts truck for a couple of hundred.