Good luck finding an original fuel tank that is not rotted out. I just modified my first one and put a tank from a mid 70s Cordoba behind the rear axle.

www.robertsmotorparts.com has a lot of stuff for that era truck. I've gotten weatherstripping and other things from them. They know these trucks.

My current 50 is on an 80 Dodge short box 4x4 frame. It has a 360, 727, 9 1/4 rear and a D44 front with 3:55 gears. Gene