Don't go too daft size wise, anything bigger than 32mm, and you can't use the airbox and will need to fit something like a K&N airfilter, I have a 38mm Keihin carb on my hybrid, works well with the engine, but was a pig to fit, plus the Malossi air filter sits at 90 degrees to the carb near my legs.
Aye, I had to modify the inlet manifold quite drastically to fit the VHSA. Took a hole saw to it. Carb sits in nicely however is not using air box.
Plus my VHSA was off a dellorto. My 4DL I sold to NEV. The Lambretta one had some subtle differences. No warmer pipes. And no oil inlet, Thank god!, since I was using the inlet oil intake.
