100 mph on a Lambretta isn't impossible, and it's been done in the past.
I've seen "road" Lambrettas in southern California that were well capable of 100 mph. Some of the ASRA racers used their race scooters on the road. I remember them carrying these little triangular side stands that fit into the crankcase lug for the rear wheel jack that they used when they parked up.
Vince Mross's Group E (Specials class) SX200 was road legal, with lights, horn, and turn signals. My friend, Dean in LA just bought the rolling frame off of him.

Matt Dawson's (and later, Vince Chu's) Group E Jet250 was clocked at the Streets of Willow, Willow Springs Raceway, at 125 mph. Vince Chu rode it in at least one rally I can remember. Scootering featured the scooter in back in 1992.


Stony Smith's (Ontario, Canada) Nitrous Lambretta street racer was clocked at 113 mph

I don't think being a "rally going scooter" should be a requirement as long as it's legally ridden on the road. Just sayin'.