A 30 is a lot of engine for that airframe. Don't forget the vibration. What good is 'saving some money' if it all ends up in a trash bag and/or destroys your servos. The YS will vibrate too, but they are wonderful engines. The 120 AX would be an excellent choice; low vibes, great power, easy handling. Good luck with whatever you choose. I've seen three of them at the field, and they all fly great with those different power systems.