A body gas tank.

You might be able to make it work. just bent the flanges in on the sides. The fill tube might be pushed into the tank. On the early years 67-72 you can take the tank out with the fill tube in it. Later models it must be removed because they are installed on the outside of the quarter.

Plug all vents on the tank and use your fill tube it has a vent on the tube. its all you need.