How big of engine is to big?
I would say go 4-stroke. i now it's not on your list but a Saito .72 on that bird is perfect. if your stuck on a 2-stroke. think about a high performance 2-stroke . My 1st choice would be a Webra .50. Other good choices might be MVVS or Rossi or Dub Jett. A.60 2-stroke would give it plenty of power, but at a wieght penalty. The .90is to big.later daveo