Your Busa's not lowered, is it? I've seen some tag mounts in that location that seem way too close to the rear tire, but I guess if they're out riding with it, it must be OK...
Like your idea of making a metal bracket for added support...
What kind of undertail is that? Looks a lot like what Mototeck used to make, but I don't think they're in business anymore (I have a Mototeck on mine)