Beer Guy: solid advice given and the right questions asked. I just replaced the fuel system on my 66 lemans. New Tank and all fuel lines, My friend said why replace the tank if nothing is wrong?
Well after 48 years, even with low mileage, something may be wrong. It certainly looked awful on the outside. hen I took off the old tank and shook it sounded like marble inside, there was no sock at all left on the sending unit, it had completely disintegrated. Used new steel fuel lines from inline tube and steel tank, filter of course etc.
I use and recommend oeitker clamps on fuel lines, they make the most uniform and secure fitting. I use two on each rubbber to steel connection when space allows.
It does matter what the car had and what lines you run. The Ac cars had a 1/4 inch fuel return line. It is liquid not vapor as some say. It was put in by Pontiac engineers to keep the fuel from percolation because AC cars dump the heat from the AC compressor into the engine bay.
I ripped out my AC, don't want it but want all that goes with it, return fuel line, 4 core radiator, 7 blade fan that make car run cool, and especially at idle.
My recommendation is to change tank and lines and system components etc.
Not easy putting in those fuel lines through the frame. but you can do it. Recommend a lift though.
Good luck, car looks great!