RE: Engines...
i run the os 61fx on my daughters pt60 and that engine has more than enough power.i like the tt pro 61 also,the tt pro weighs 3oz more or so than the os fx but with this type of airplane i don't think it much matters.my daughter learned to fly on her pt60 it has good tendency's,i built her's and put less dihedral into it IMO handles a bit better.