Having a couple of Bud Nosen planes myself, I would recommend a 1.20 four stroker or a 26cc gas engine. If you install a .90 four stroker you would have to fly close to WOT, you would actually use up more fuel in a .90 at WOT than a 1.20 four stroker at 2/3 throttle and they will fly the same. That is why I use 1.20 for stroker in my quarter scale Cubs and the like. I leisurely fly for about 20 minutes on less than 16 oz of fuel at 1/2 to 2/3 throttle.