Back in the 70's, some a guy from Southern California rode the Baja 500 on a Vespa Rally 180. From the photos of the scooter, he didn't really do a lot to modify the scooter. About all I could see was a legshield mounted spotlight, and a modification to the exhaust to have it go up and over the motor. I think he also removed the front mudguard. Needless to say, he didn't finish the race. The only information I could find on it was that he had "carburetor problems."
Well, the Baja 500 is now the Baja 1000, and it is mainly the purview of big race trucks, and off-road motorcycles. Some guys think that they can do it on vintage Vespas. I wish them luck. The video above was about the only thing I could find on their site. I think it is the jalopy that one of the guys plans on riding. I'm guessing this is the pre-modified scooter. I wonder what he plans on doing to it!
You can find more information on their preparations here at Scootin the Baja 1000.