I thought the purpose of the Sportster 65 was to power RC foamy Mig gunnery target drones. It seems like the bulk of them out there were salvaged from the drones.
The problem I always run into with any of the "other" engines, that may be less popular or simply unknown quantities, is that I don't want to take the time to build a real stunt plane around an engine that might not work. I'd rather spend that time building for an engine I know will run well and work out in the end. The engine is the cheap part compared to the time and raw materials spent building a 60 size stunt plane.