It depends on what you mean by "restore". Ideally you remove the body and suspension, blast the frame, etc. Assuming you mean local areas, you could grind/sand to a clean/cleaner less-rusty surface and you can apply naval jelly (phosphoric acid).
If you can remove the body areas and sand very, very well, you can prime and paint with chassis paint.
If the rust on the frame is bad to the point of weakening the frame, there not really much that can be done other than swapping for a better frame. Anything more than surface rust should be evaluated to determine how much it has weakened the frame. I've run into several trucks that have rusted frames that were useless as well as many suspension mounting brackets that were rusted though. Rear spring hangers are especially vulnerable to this.
The engine bay and front suspension parts on my truck was in great shape. So much oil and hydraulic fluid leaks plus road grease kept the entire area coated lol. Now I worry it might start to rust with having fixed everything
After I cleaned everything I sprayed mine with Miracle Paint. I used it on the frame, underside of the bed, underside of the cab, and sprayed the floorboard too before painting.. Damn good stuff, It's what I will be using from now on on every truck that I build..
RamchargerCentral.Com is a Dodge truck community built by a vast number of experienced owners. Whatever you're thinking about doing from routine maintenance to full-on restoration, odds are somebody around here already has. Originally focused on the Ram Charger / Trail Duster, our members own, drive and wrench on Mopars from the 40s to the current day. It's not what you buy, it's what you build.