you can swap in a mustang tank and they're pretty cheap. http://mmb.maverick.to/showthread.php?t=35490&highlight=gas+tank
A 65/66 mustang tank should fit i would put a ruller on it first i have a 71 i put a 15 gal fuelcell in mine i went to a fab shop an thay put a 45deg neck on it so i could use my filler neck it works fine