Lifer,
Due to the size of the AT6 I do not think that gas is the way to go. I have looked at some of the smaller gas engines and with the carbs and mufflers sticking out the way they do you are not going to have much cowling left by the time you get the engine mounted. I am also concerned by the weight of the engine and since they all have EI you have the additional weight of the batteries. Given that I do not know what a 'rcgf' engine looks like I would stay with what has proven to be a great combo for this plane, that is a nice 91 four stroke. You other guys care to comment?

Maddieone