I was going to restore my 79 Ram until I seen all the rust. When I started tearing it apart the rust was so bad that I am pretty sure it is beyond repair. My questions is can another cab from a 1994 or newer dodge truck fit on my chasis? THANKS!

Actually, the cabs, beds, fenders, etc... can be swapped around from 72-93. There are a few things to watch for.

the Dash layout changed in 81
the 89-later cabs have some minor provisions to clear the CTD platform
the roof will look slightly different
72-80 doors/fenders have different body lines than the 81-93 doors/fenders. If you swap to the later doors, you have to swap to the later fenders as well, or the upper body line will not match up....but the completely bolt up with no issues.
Make sure you use the correct rad support for the grille you want to use...there are several variations.

the cabs, beds and fenders will bolt right up to earlier/later frames. there are some minor differences, but overall, they are pretty much interchangeable. :waev:

he covered it quite well....

Yeah, Mike covered it pretty well!

Welcome to the late 70's trucks! Actually, the whole line up were rot boxes and poorly designed. All marques had their rust issues, but the Dodge sheet-metal seems "cheaper". I make this observation by actually having the different brands of trucks of the similar vintage parked side-by-side.

Fixing the cab rust on the Dodge trucks is pretty easy to do though. But the one place that's really critical, and NOT an easy repair, is the rain gutter above the drivers windshield. Heck, even my brand new (at the time) 1990 Ram truck started to rot up there in 4 years!

The rest can be fixed, and parts are there to do just that. I have drawings for the inner rocker panels and seat supports, which are two items that usually need repair, but nobody makes. If you want them, just let me know and I'll send them to you. Have a local shop make them for you!