We had one on 75 2 litre- Weber dual throat and went very well . Slight hesitation sometimes at varied rev range under quick acceleration but improved performance-not a lot but noticeable and slightly more fuel .
Not having a go, but a search will find a lot of stuff about weber progressive carb conversions. From my own experience they are fine when running well but suffer in cold weather because the intake runners are long and made of steel (poor heat transfer). I used an adapter to put an air cleaner from a Mazda on mine to get warm air in and it helped a lot. I also had a lot of problems with vacuum leaks that were partly related to the poor fit of the manifolds to the head and partly to the rubber boots perishing. I suspect the latter was also related to the poor mounting of the carb plenum (under the carb) which allowed the plenum to move wrt the intake runners when the accelerator cable pulled on the carb.
Given the money I would first go for twin Dellortos or twin throat webers, then twin, single throat, then the weber progressive.
i was reading a pomy vw mag the other day, according to them, and it makes sense to me from what they've said, a set of dual dellortos. They are hard to find these days, but places do sell reco'd ones and parts are easily available. Better performance and fuel economy depending how you are with your right foot.
