Have you looked at an Ercoupe fuel system? Two wing tanks in common
(IIRC), pumping with a mech. pump, continuously to a small (5 gal.?)
header tank. Header tank overflows back to a wing tank when it's full.
Header tank feeds the engine via gravity flow.
When the wing tanks are empty, the header tank float & wire gauge
begins to drop. At the moment, you know exactly how much fuel is left.
Works excellently and is very simple. If the pump fails, you still
have the header tank.

Rich S.