Gene, it didn't mater much, I still had to mount the engine and there was no room for the GP mount so I had to use my grinder to make the mount fit. Then I made the cowl fit the engine, sort of built it around it and hogged out the inside of the cowl. It was tight. I only have one plane with the engine mounted upright and there is no way to deflect the exhaust so it is a real slime ball at the end of the day. I pretty much never mount an engine upright. Side mounted makes for a better shot at the throttle too.