I started (and finished) a GSM project about two years ago. Back in the day, I passed on the thing, because they were about $3.95 or $4.95 and you could get a double VooDoo or Combat Cat for the same money. Upon enbarking on the project, I found that the (required) VooDoo-style leading edge goes for the same money and typically weighs 3-to-5 ounces. I Dremmeled out a few tenths from the back of the LE before assembly.
Anyway, I was able to borrow a prototype from Currell's extenive stash and create a nice copy.
This is certainly classic-legal and also maybe OTS. The 40" Stuntmaster was listed on John Miske's GSCB holy writ of OTL designs.
It's been a very successfully sport plane, racer, engine tester, and Classic Stunter for me. Walt Musciano autographed it for me at Kalamazoo.