I don't blame you for wanting to fix it especially if you are retired. The best advice for many is to get a better cab. But you can eventually replace the metal. Classic Truck Parts of America, and others, have every possible patch you would need.
A few thoughts of my procedure: Do as you wish with your experience and ideas:
1. Hang the doors and adjust a little to get the proper gaps. This is probably the most important thing. All the other repairs kind of effect that opening. So get it right and brace it with temp struts until all work is done. Try to do the hinge/hinge pin repairs, then hang doors, then adjust, then brace, then weld. Don't forget there will be rubber seals between the doors and the cab.
2. The rule is: only replace the rusted metal, even if you only use a small portion of an aftermarket patch panel. Leave good solid metal alone. You may have to body-work some portions before patching an area.
3. Back up your welds with copper plate.
4. Try to get cab high up on a dolly so you have seated access while welding. Lay it over to expose areas you need to weld if you can.
5. Practice on the cut out pieces and the left over patch pieces every day before welding. You should try .025, .030 and .035 to see what you and your machine likes the best.
6. Don't forget, while you are cleaning the metal around where you are going to weld, to clean a place for the ground clamp.
7. Chase ALL threaded holes on cab. Repair ALL weld nuts and captive parts.
8.
Take your time. Measuring other cabs is a good idea. Get a good die grinder for cutting out rust and a good angle grinder for cutting and grinding thicker metal.
9.
Take your time on each spot weld. Don't get in a hurry. Don't do any bead welding, only stacked spots.
10.
Take your time and practice a lot. Nothing to be intimidated about, yet! One of the suggested donor cabs said "good cab corners but floor needs work". You want the opposite of that or all good metal. Why would you buy a donor with bad floors?
11. Know when to give up and buy a donor. It actually may be much cheaper. There is so much to do on restoring that truck that you don't need to fight patching and have a nervous breakdown because you think you are enjoying welding. Of course you want to find one fairly near you so you have a chance to Uhaul it home. I looked at Craigslist Indianapolis and found
this. Not bad price with a door and fenders included. Good collection to have around but not sure of floors.
