Online Community of Zenith Builders and Flyers
It has been done over and over. Look this site up : http://mthobby.pcperfect.com/ch601/chengine.htm
There you will see Michel who has done it from scratch. He's flown his 601 for 400+ hours with the Subaru engine.
He has a very detailed website on the conversion.
If your into that sort of engine I'd look at the corvair as well.
http://www.foxcon.com/Subaru-EA81.html try this link.