I bought one of the underbed gas tanks from Tanks Inc. Really like it a lot. It was a perfect fit, no adjustments needed. We got an aluminum tank from them. Putting the gas filler in the bed.

https://sites.google.com/site/bluejaygarage/home
53 half ton http://s159.photobucket.com/user/sworden73/library/?sort=3&start=all&page=1
72 Nova SS sold
75 Corvette
52 Chevy Styleline Coupe