I know it's not a 59 but, I modified a 71-73 Mustang tank to mount at the
rear of my 52 panel. I needed 20 gallons capacity and a shape that was a good fit
for the rear of the panel (where the spare tire would go. Had to weld up the original filler hole & moved the filler so it would be accessible through the floor
in a recessed housing that's vented at the right rear of the cargo area.
I don't know if you wish to change the location, but I can tell you the tank fit perfectly and only needed to extend the Ford holding straps slightly to attach it
securely. If your rear frame dimensions are similar .... it might work for your TF truck, too. Cost from a discount place online was about $110-120 plus some filler bits I got off of eBay .... whole job was under $140.
