Hi Rob,
The bike is going perfectly 6000km later. I decided to stay with the original carb, just jetted it to 105 (I think) as the torque low down issue is really only for a second off the mark. If anything, it's even better now than when first built. That could be the belt and rollers settling in. Full throttle gives between 8900 and 9100 rpm with the Malossi variator and 12.5g weights (a mix of Vespa 11g and Malossi 14g). It pulls strongly and sounds very sweet at that. It is still as smile inducing as ever and I ride it most days
It is because everything else is so sweet that I chose not to risk all for a slightly better launch to 30kmh. If I roll the throttle on from a standing start it gets to clutch lock just as the rpm hits peak HP so it's not an issue really. The lighter variator weights do pull the rpm up at light throttle more than is needed, but not so much as to be irritating. light cruise is about 6000rpm, deceleration 4500, and full noise 9000.
This really has made an extraordinary difference to the bike. It feels slow and scooterish (and safe) up to half throttle, then snaps into tune the way you would expect from a tuned two stroke at about 2/3 throttle. The exhaust note changes to an encouraging roar and she's off. Vespa should have built them this way from the start!