I think both engines you mentioned would be good choices. I flew the CMP F6F for a year with a Super Tigre G2300 glow engine. It was far more power than needed for the plane, but the short nose moment requires some weight to balance, and I chose to use aluminum instead of lead for weight . If I do the F6F again, it will be with one of the 26cc gas engines available. The cowl is spacious and will contain most engines, completely.