With the specs given I think a 120 4-stroke is the absolute smallest engine I would use. A gas engine would be great but I fear a tad heavy. I think for best performance the Saito 180, YS 140/160 or the larger 2-stroke glow (O.S. 160 and Moki 180 for example) is the way to go. Personally, I would love to have one with a Brison 2.4 or ZDZ 40 as long as the weight could be kept down. Time will tell.