2 st and 4 st may run the same inverted but that is the trick, to get the 2 st started without flooding. When inverted, the fuel has a tendancie to pool on the glow plug in a 2 st making it hard to start. Whereas, a 4 strokes' glow plug is on an angle so fuel has little chance of pooling thus making a 4 st a better inverted choice.. That being said, it is also more difficult to install and remove your glow ignitor from an inverted 2 st so a remote glow ignitor may have to be installed. Tank height will also be very imortant. In a lot of 40 size planes it may be very difficult to get the tank down low enough when trying to invert a 2 st. Another viable install option for an inverted 2st, is to install it about 5-10 degrees tilted to one side as this will greatly decrease the chance of fuel pooling on the glow plug and make starts easier. Like I stated earlier, I prefer a horizontal or upright 2 st for simplicity and less fuss. Each to their own!!!!!

Curt