If you want an interesting project (albeit non-rotary) you could try a Corvair engine. I have two neighbors building with the 100 hp version, with one putting it in a KR-2S, and the other is taking C-150 pieces and attempting to make a tail-dragger version that is light enough to meet LSA rules.
Seems like it could be an okay way to go if your single rotor experiment doesn't work out.
Hi Doug,
Thanks for the thought, but I don't have any interest in the Corvair conversions. Some people swear "by" them, and others swear "at" them. Not much in between.
At the moment, it's neck and neck between trying the single rotor, and just installing an O-235. I'm sure there's far less pain and suffering involved in the latter, but that may not stop me from trying the former :-)
Rusty