if pushing the limits on ground clearance maybe think about a skid plate or skid rails under it. better to bend a skid plate or rail than cut a slash in the gas tank.
what have you got for room behind the axle? possibly a tank from another vehicle, like an S10 blaser or something would fit back there and fill from the side?
here is a thread for 55-59 trucks talking about options
http://67-72chevytrucks.com/vboard/s...d.php?t=574762