I had an OS 120 Surpass III on a 12 pound Top Flite P-47. The engine flew the plane with authority. If want to fly scale, just throttle back. IMHO a warbird weighing 10 or 11 pounds with a 65" wingspan is normal. Most warbirds need nose weight so it is normal to put the biggest engine you can in the nose of a warbird. If you ask this question in the warbird section you will find that most people will recommend at least a 120 four stroke. Oh and by the way, never use flaps for take off. If you do, you will not have your warbird for long. You want to build up as much speed on the ground as you can before you become airborne. If you do not have enough speed, the plane will tip stall faster than you can react.