RE: .52 or .70 4-stroke on Trainer plane?
Prefered engine would be an OS 70 or 52 four stroke.
The two configurations I'd expect to use it in would be:
1. My winter-plane project. Perhaps a high wing 40 size trainer, a 4*40, sportster or stick type of plane with skis.
2. Warbird, I think the future home for this engine will likely be a warbird ARF. (Some 40 size warbird ARF from World models or Great Planes)