I run almost all of my 40+ engines upside down ( inverted ), both gassers and glow...

Those who claim there are problems doing so, don't know how to tune or set up their planes/engines.

Inverted glow engines do have a SLIGHT tendancy to pool fuel in the glow plug, but this normally happens when the engine is new and thereby out of tune.

Once the engine is properly tuned, fuel has less of a tendancy to flood the head with the needles properly adjusted and the throttle at idle.

An inverted engine has a slightly tighter tuning window, but this is not a big deal. If anything you'll get better at setting up your engines than most.

Just remember that you normally do not need to prime an inverted engine prior to starting and you'll do fine.

Fuel tank height only affects the engine when the plane is sitting on the ground with the engine off. Fuel can siphon into the plug, but if you keep the throttle fully closed before starting that will stop or minimize. Once running your engine should not care if it is upright nor inverted.