I did a Toro 25cc conversion about 3 months ago. I did send the cylinder to Scott Ellingson to port it. So far I have less than $150.00 into it with the CH ignition. It turns an honest 8850 rpm with a Master Airscrew 16X8 and idles at 1500 rpm all day.
Check out
www.scottellingson.com he has ready made motors very cheap and ready to run.