RE: Another "What engine" question for a 4*120
Usually this plane builds tail heavy, so the added weight of a little gasser is no problem. The only dievation will be placing the firewall a bit back from the plans which is no big deal. My 4*120 came out at 12 lb with the RCS 140 that weighs a tad over 3 lb, and swinging a 16" prop is about as big as you can go without longer gear.