I thought my cab has too much rust to save..now I'm grateful that I only need the bottom 8 inches of the entire cab haha! If its not a original paint patina masterpiece and you are going to prime and paint it, swap the cab. It makes sense from every angle.
Nostalgia wise, its totally still the family truck. Just consider sheet metal from 70 years ago as consumable as batteries and belts. Eventually things need to be replaced, right?
As far as the VIN, you are definitely NOT going to patch in old VIN into the new cab. Nope. It's okay everyone, he isn't doing that