Sorry I took so long to respond, I haven't gotten the chance to get online today. To be specific, the Polini kit I have is 57 cc. (Bore=41mm, Stroke =43mm). This kit is bolt-on. It requires a plug that is one step colder than stock, but uses the same carb as original. Mathematically, this amounts to a 14.5% increase in power. It is noticable on hills and accelerating. When I put the stock pipe on, the rpms don't really change, but the power is better. When I put the performance pipe (expansion chamber) on, the rpms increase by perhaps 1000. You can hear a difference. I go up one jet size when I use the performance pipe, but not when I have the stock pipe on, and it seems fine. Also, with the bigger jet and perf. pipe, I run a more open airbox, although I'm not sure it is necessary. Basically, if you are not changing pipes, you probably don't need to make any major changes--perhaps just a change in jet. It will tell you which jet to use in the instructions based on your combination of pipe and cylinder kit.
Let me know how it works.