I have a plan I drew up for the R3 which was posted on another forum for a long time and seemed popular. It's a 76" span model but don't let the WS fool you into thinking its small as the fuse is as big as any 50cc bird out there.
The basic specs are :
Engine range 30 to 40cc
Weight dry: 12 pounds (with a 30cc engine)
Construction is balsa, ply and foam. The wings are built up from wood.
Details on the plan are not as high as those on the 40% Monocoupe I posted in this forum earlier as my intention was to build it for myself which I did and only after, did I decide to share the plan, but if you know how to build then this wont be a problem for you. There is a certain amount of fiber glassing work required for the cowl and wheel pants but nothing overwhelming. Foam parts are sanded to shape no foam cutting rig is needed.

If your interested in this let me know. My email is [email protected]

Pete