I'm only about a week away from departing for the FF World champs, so have no intention of trawling through dozens of back issues of MB or MAN to find the specific article and plan. My gut instinct is that it was in Model Builder not MAN-but I could be wrong. Someone here will recall the name of the design, and the appropriate issue. then its over to Sport Pilot if he likes what he sees. I don't know what the current status of the MB plans service is-Bill Northrop died a couple of years back. I'd just be inclined to scan the plan from the mag and have it enlarged by a copy shop to the correct size.
Fortunately-a google search under 'Bill Cannon' means I don't have to-the design mentioned above whose name I could not recall is the Griffin III and Griffin VI-it was published in Dec 1982 Model Builder, in two versions-one for .03 and one for 06-28" and 36" respectively............and better still, you can find the plan in downloadable form at www.outerzone.co.uk
and I happen to have that issue of MB and can scan the article if needs be