Do you have this set-up at the rear on the opposite side from the fill neck?
My '70 has this but also has about 4 or 5 rubber lines directly below it under the bed.....I filled it up and gas started pouring out...all of the rubber was dry rotted and cracked. I replaced them and that stopped the leak(s).I do have the EVAP canister but I still haven't figured out what all these lines are supposed to do?