I have an FA150 mouted inverted. I'm running C&H electronic ignition, but fouling the sparkplug is juat as much a concern as a glow plug.

I rotated the engine slightly to have the exhaust valve @ 6:00 o'clock when the plane is sitting level. W/the exhaust pipe running down out of the bottom of the cowl, any oil tends to collect @ the exhaust valve & it is expelled as soon as the engine is turned over.