The Avid Flyer STOL Wing is already an excellent STOL wing, doing most everything the STI wing does for the newer Kitfox. If you could fit an STI wing onto an Avid Flyer, which probably could be done with some fabrication, I doubt you would gain anything over the Avid STOL wing.

Trent Palmer did an ecxellent youtube video recently describing differences between a Kitfox STI and a Highlander. That would be a great video for you to watch as the Highlander wing is nothing more than an Avid STOL wing.