Rusty:

 

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.

 

Doug

RV-9R, 13B

OK City, OK