I do have suggestions but not sure what you want to do. You say your wiring is basically OK with some bad terminals. Then you say you want to do 12V with alternator.
I always recommend 12V with alternator.
Let mine know if you just want to do 12V with Alt and fix a few wires, or you want to completely rewire. If you rewire, you definitely want a prewired fuse panel type kit.
Click.Fixing the "bad" wires and adding Alternator will be pretty low cost. Don't do the "one wire" type alternator. It would also be nice to get rid of the ammeter and use a volt meter instead.
Don't know your experience level with wiring. But enthusiasm and willingness is as good as experience. Wiring is not hard to do an an old truck. We will help all the way.