Will,
Jim Carter Classic Truck Parts sells two gas tanks that will work for your truck.
The first tank has a part number is MEG160 and is a 13.5-gal. aftermarket direct replacement for the 1947-48 pickup and 1947-55 panel suburban trucks. It goes for $525 and can be found on page 109 of the JC 1947-55 parts catalog.
They also offer a "street-rod" 20-gal. under-the-bed tank for your truck as well. It is part number MEG161 and goes for $550. It is also on page 109 of the JC 1947-55 parts catalog.
Good luck on your project!
