Depending on which gas engine you choose, it could be an option. The EVO 26GX weighs about the same as my OS 1.60 (add a few more ounces for the ignition unit and battery). I could see one of those working. The Zenoah G26 (engine only) on the other hand weighs about a pound more. You would have a challenge ballancing the plane with the extra nose weight using the Zenoah. The extra weight of the ignition on the EVO 26 would be countered by a need for less fuel. In reality you would likely run the same size tank, but would get longer run times. Power would be quite a bit less than the glow motor, but I normally run around at 1/2 throttle anyway to save fuel (and the plane will fly at 100mph at half throttle). I doubt the EVO 26 would vibrate any more than the same size glow engine. So to clarify I would say a light gasser should work just fine.

As for flying fine at 17.5 lbs, it might. I for one would not like landing the plane at that weight unless I had a fairly long and smooth runway. I take off at about 16 lbs, but with the fuel burn I land at closer to 15.