I don't think inverting the tank is a good idea and it will not help. You need the center line of the tank close to the center line of the needle in the carb. If you are running tank pressure that can help a little.

and like it was said a pump can fix the tank issue.

If you can keep from putting the engine completely unside down, like move the head over a little off inverted it will help a lot. 15 degrees or more makes a big difference. I did a satio .50 like that and it worked well.

another problem witha inverted engine is exta fuel running into the engine can put out the glow in the glow plug. A lot of inverted engines ( again the ofset 15 degrees helps ) have to have a on board glow driver to keep the engine running through out the flight.