I agree this borrows nicely on automotive muffler design, but more on the turbo mufflers than Flowmaster (though the deflectors Chris mentioned are of that thought process). Really great work, especially since you did it some time ago. And I think the workmanship is pretty amazing for a prototype you were developing...looks a lot like some of those welded drag car mufflers.
I actually asked the Flowmaster guys a few years ago why they didn't build bike mufflers and they shared they had but they failed. Said they initially targeted Harley's and there were 2 issues. The first was what was mentioned, those people want the loud pipes. The other they claimed was this is a much harder problem with a single cylinder engine (we were talking thumpers) than a multi-cylinder due to less pulses that can cancel each other out.
Doug