I allways try to have just a little more power than needed, you just never know when that extra power can save you untill you need it. Allso most 1/3 scale cubs that I have seen or read about
use at least a 45cc on up. you can see what your plane wgt is before you add your engine, If it's around say 24-25 lbs I would go with a 50cc or larger, you can allway throttle back once airborn. Hope this info helps.