I need an airplane to hang one of the bigger Honda 4 strokes on - GX25,GX35 or GX31. It doesn't need to be aerobatic, I'll be using an overpitched, oversize prop for some testing purposes. So just an airframe that's big enough for the power, reliable and straightforward for someone of marginal skill (not quite a beginner, but only a year or so experience) to fly.

Any suggestions?

At first I thought a Cub as it's pretty easy to fly, but with high pitched/diameter props you might want something a little more streamlined. A .90 size or bigger sport model might be the direction you could look in.