Cubs are pretty flexible in terms of power. It would probably fly just fine on a tired .60 two stroke glow engine. You might get away with as little as a .72 four stroke glow engine but at ten pounds you would just be putting around. It probably wont fit the cowl very well but you could probably hang a 15-20 cc gasoline engine on the firewall. Once you get past the point of enough power to fly it then it becomes a question of how hard you want to push the airframe.