Let me ask the original poster for clarification. Is the centerline of the tank one inch below the needle? Or is the top of the tank one inch below the needle? Which it could be, if he mounted it under the tank compartment instead of in the tank compartment. In which case it would require some fabricated covering, but I'm just asking.

If the centerline of the tank is one inch below the needle, and mixture is adjusted with the plane upright, there will be a problem in the air when the plane is flown inverted. The mixture will go rich, and probably kill the engine.

If the top of the tank is under the tank compartment, use a smaller (probably round) tank and move it up into the tank compartment.

If the tank is in the tank compartment, and the centerline of the tank is one inch below the needle, that tells me this thing has a big oversize engine, mounted upright. One solution might be to re-mount the engine inverted.

Good luck
Dave Olson