I have one on my to build list also and I'm planing to use a .60 2 cycle (probably OS). I have a buddy that had the red box p-39 that weighted 10.5# and done up very scale like and it flew with a non schnurl .60 and flew very well (1970's vintage). It did not have alot of vertical but neither did the real one.

Just got the nose gear for this one on saturday what a steep price$$$$

Good luck

Jeo Felice