Jeremy,
At the risk of getting hunted and burned at the stake by the purists, I say do whatever you like man, its your truck and you know what you are going to use it for. Using a modern chassis and driveline would probably be ideal, but I'm sure the old timers who purchased these trucks to begin with used em to haul, pull and tow more than they were ever designed to do. I know the trucks on the farms were basically loaded until you couldn't load anymore no matter the weight. They won't go fast, handle well, or stop well, but will get the job done. Let us know how it all goes, post pics of your project as you go and let us follow along. The main thing is to enjoy these old trucks.