Best ARF combo I've see so far is the H9 UltraStick.
Here's a thread with converted Ryobi...looks sharp...

One of the secrets is to look at the WING AREA...
GO for about 1200 square inches if you can...

With the Ryobi 31cc conversion, I would bring the nose back about 1-2 inches though...easy modification. And put the elevator and rudder servo in the tail.

http://www.jagengines.com/Ultra31.htm
http://www.modelairplanenews.com/reviews/ultra.asp

A good thread here on one...
http://www.rcuniverse.com/showthread...01&forumid=257

Good luck!
CrazyHerbb