Check out the hall of Fame section of Stunthanger and Allen's bio. It has the complete bibliography of what he had published. The Opus was in the British mag, Aviation Modeler International. They should have the plan and perhaps you can find that issue on eBay. He Had designs published in all of the major mags, M.A.N., Model Aviation, Flying Models. I wonder how he found the time to do them all!
Type at you later,
Dan McEntee