It will help let any vapor bubbles burp out. On a system with a vapor return in the fuel filter, the return nipple should be clocked at to be at the top. Those sometimes were run horizontal because the relief was in the return. A '72 car came with some version of the 'vapor saver' systems. Its worth seeing which one is on your car, read up on how it works, and then figure out how to adapt or modify it so it works with, not against your current needs.