The hole on the rear of cab (where a seat belt might go) is curious. They dont rust there. I suspect you have a big nest up in the roof and the rust is caused by something that was living up in there. Poke around up in there.
~ HB 1966 Chevrolet K-10 | Ghost: formerly Flappy Fenders | In the Stovebolt Gallery 1962 Chevrolet C10 1962 Suburban