JM $0.02. If you plumb the vent of the main tank to the engine exaust, you will pressurize the main tank to feed the head tank.

I bought a used Cermark Pitts Byplane with the engine mounted sideways. No one could keep the plane running going inverted. The problem was the tank was way too far below the engine. You had to run it really rich to get it running and keep it running upright, but when you rolled inverted, the tank was way above the fuel inlet and it would blubber rich and die. You could not reposition the tank, due to fuselage design. The cowl was already butchered for the sideways installation.

There was room in the fuselage for a head tank, above the maintank mounting platform. I installed a small two ounce dubro tank above the main tank, the header tank fed the engine and got replenished by the clunk line through the small tank vent by pressure from the muffler going to the big tank vent. This allowed the ST2300 to see approximately equal pressure both upright and inverted. This system works so much better, but hind sight being 20-20, a pump/regulator would have worked fine also.

Happy Landings.