I have HEARD (key word there) that comet 30 series can handle more power than its rated too, but not sure how much that is, or if its true at all. I know a member had problems with a GTC (not comet) 30 series on a 9hp. maybe blaz has some more info on the subject.
i would try it, worst case scenario you need a new belt, but have an extra 11hp engine! (excellent deal on that engine, if you got the cash to spend, get it!)