If my GX670 proves too small, I will consider the Briggs 810cc vertical crankshaft model 49T877 on sale for $959 at Northern Tool. The vertical needs conversion to horizontal, but should be doable. Briggs are good enough for aircraft, I feel. (used in France and Europe) Direct drive can only produce less power than typical use. So should be fine if crankshaft doesn't break from prop torsional dynamics. All conversions risk torsional vibration. The thrust bearing should be fine.