You could go to the pre- early '49 style which is between the frame rails under the bed. I suspect a good donor would be a **** Ranger or van which have long skinny tanks that fit well under the bed. A Jeep CJ or YJ tank (or two) would work well too since they are easy to get ahold of and they fit between the frame rails. You can get them in aftermarket high capacity versions in metal or plastic.
