I am running a Saito 100 inverted in an H9 P51 with no reg or on board glow heat. It does not suffer any related fueling problems. It has been fairly reliable and mostly trouble free. Only 2 flame-outs in its 10-12 hour life so far.

The OS .91 Surpass 2 Pump is an extremely reliable performer in an inverted mounting at any orientation relative to the tank. Mine (inverted) has never had a surprise dead stick in 80 or so engine hours.

The YS FZ line is very good inverted too. Again, no need for regulators as they are part of the deal.