Found a 54...

[Handfull 54]

You should check that frame you bought because 54 frames are different from 47-53 frames,especially in reguards to mounting the bed. The beds do not interchange. Perhaps someone has put a 53 bed with a 54 cab and can shed some light on if it can be done. I found out with my own truck that it's cheaper to get some new or used solid inner fender wells as you will spend a lot of time fixing ones that are swiss cheeze. If you have more time than money then have at it.