Can you swap a 2004 ram 1500 cab with a 2003 ram 3500 cab that had the cummins

 

Moved to the correct section.

 

Yes, just about all the body pieces are interchangeable on the third gens. I can't remember what year they did it, but I seem to remember there being some kind of body line alteration being done so you may want to make sure your two cabs match before you plunge in. Keep in mind, you're trying to put a gas cab on a diesel truck. You'll need to swap your modules and cluster over and you need to ensure the wiring matches. Otherwise you may have a code list a mile long and/or some things may not function. This includes SKIM for any chipped keys. For example if your truck has SKIM but the donor doesn't, it won't start (or start and shut off) because the PCM hasn't gotten confirmation from the SKIM. Same thing vice versa, or if they both have SKIM you will need to transfer your SKIM over to match your PCM.