I've not used the Polini PWK, but there are other manufacturers that make PWK carbs under license besides them.
I strongly suggest you invest some time researching the internet for information of how they should be 'blueprinted' which includes setting the float, ensuring passageways are adequate etc. I'd be very surprised if the Polini needs any modifications.....
That said, it is very worthwhile modifying the floatbowl so that the pilot jet is removable without having to remove the bowl itself. You can see how this can be achieved via:
http://www.mid-atlantictrials.com/Instal.htmlI think the PWK carbs are
extremely good as they are easy to set up, are relatively inexpensive, work very well with an adequate air filter & do not have any tendency to flood (built in float bowl overflow), unlike one round slide type that is extremely popular with many lambretta users.