Hi Bud

I used Hitec 625MG servos for all of the control surfaces and a standard 422 for the throttle.I also used an 1100 mil. Ni-Cd pack mounted under the rudder servo to balance the plane.I think with the extra weight of the engine I used that the plane is probably on the high end of the range for this plane at around 15lb. or so, but seems to fly just fine at that weight and slows down OK for very smooth 3-point landings.I think Hitec 605 servos would probably be the minimum for this model.A lighter weight 2-stroke or 4-stroke single used would also result in a lighter aircraft.Hanger 9 used both a Saito 180 and a Zenoah G-23 in their prototype planes.With a G-23 it would weigh even more than my plane so weight is probably an issue only depending on what kind of flying you want to do and how difficult the plane is to balance with the heavier gas engines.One of the new lighter gas engines such as the RCS 140 would also be an interesting choice.