This has to be a hybrid, right?

My thought, also.

 

Certainly the filler location is not original. Hard to say what the PO did without taking off the diamond plate. Other cues on the body (windshield, seat brackets, lettering) look right for a '75, and a '75 would have come with the rear tank.

Adding the under-seat tank to an intermediate is really easy - basically all Jeep did when they moved the tank to the rear was to remove the under-seat tank and stop punching the hole in the side of the body. A tank from a late '60s CJ fits with only drilling holes for the straps and the fuel line, and cutting out the recess in the body. I used a sabre saw (jig saw in some parts of the country) and glued in the filler neck piece. I painted with one of those little cans of touch-up paint and walla - almost double the fuel capacity. Everything I needed was purchased off the dealer's parts department shelves, including the tank switch.

 

Sometimes not so quick. Back in the 70's, a good friend of mine was cut off on the freeway and rolled his 69. The gas cap was ground off when the Jeep was on the drivers side. He ended up side down, belted in, while the tank drained out on him. About the time we was finally able to unbuckle, the gas ignited. Second and third degree burns over 85% od his body. He died after a very painfull year at age 22.

 

I plan to pull off the diamond plate anyway and see what is hiding under there. Not sure why the PO relocated the fill location from the rear to the side. Should know soon enough. There are plenty of unusual mods with the rig but mostly electrical which shouldn't be too bad to square away.

 

Not illegal where I live. However, it is illegal to shoot tracers into the gas tank of a passing vehicle so we're still safe without another silly firearms law.