As far as pipes go, this vespa simonini pipe can be made to fit w/o too much hassle. You lose your center stand and have to cut one of the center stand brackets. You just cut about 1.5" of the stock exhaust header and that acts as the exhaust nipple needed to mount the pipe.
You could also try to fit a PHBG w/o the malossi kit if you are able to find the flat top for the phbg. Maybe Dellorto Direct?