It's my understanding that '65 GTOs do not have a return fuel line however, mine has two steel lines that appear to be original. It has PS, PB, AT, factory AC. One line measures 5/16" O.D. And connects to the fuel pick-up/sending unit in the tank. The other measures 1/4" O.D. I presume the 1/4" line is a return line but do not what it should connect to on the engine, i.e. Fuel pump, carb? I do not know the purpose on this return line. I bought a new fuel tank sending unit but it too has provisions for the return line. My plan is to block off the 1/4 line but just wanted to know why it's there and what should it connect to. My car also has vent tube near the gas filler tube so I would think the 1/4 line is a vent line(?). Any advice on this is greatly appreciated. Thanks!