I,m currently working on an UltraStik .40. I put a new Irvine .53 on it because it fit the metal engine mount perfectly, I drilled and tapped the mount instead of clamping the engine on. So far that is the only thing I've changed. I'm still thinking about whether to use the full length ailerons or the split ones, I have the split setup on my Big UltraStik but have never flown it.