Those are built on a longbed chassis with a short bed right? If so then an exhaust system from a miltary diesel longbed truck will bolt right on. Not sure how many of those extra cabs survived, but most are in the midwest. I've never seen one in Arizona,Nevada,Utah, Oregon, Washington,Montana, Wyoming or California. Nor have I seen any in Ohio or Michigan. It would be fun to find out how many were actually manufactured and by whom.