You probably have an air lock. Loosen the heater return hose just enough to let the air out and then tighten it back up. Be careful that you don't get burnt when doing it.
When you are talking about a truck that age you go by the condition of the individual trucks not the brand. Either on could be in pretty good shape or either one could be a piece of crap. As far as the mechanical part they are both easy to work on.
It needs oil added or it's going to ruin the engine. I would put high mileage oil in it but that won't stop the leak. All you can do is keep adding oil when needed or have the engine rebuilt.
The cable runs to the back and there's a Y there that then runs to each rear wheel. On that Y there should be a nut and thereds to tighten the cable. Spray it good with WD40 because it will be rusty.
You are going from a front wheel drive to a rear wheel drive. You are looking at a lot of work with a fully equipped shop and a ton of knowledge needed. So the answer is one hell of a lot of work.
The plastic tank is for expansion and contraction for the antifreeze. The radiator goes across the inside of the grill. There is a cap on it that you push down on and turn to get it off. Don't remove it when the engine is hot. This is where you should have put treatment.