Li 125 S3

Just getting to grips with my resto project.... Looking to buy a 175 kit to gain a bit more power and looking to put the 22mm carb on along with a new exhaust. I have been told that with the carb I can utilise the jetting for a standard 175 ? My main question right now is that I am hoping to use the existing original gearbox. Am I ok?
Also what exhaust system do you chaps recommend for this setup ???
Many Thanks
Also what exhaust system do you chaps recommend for this setup ???
Many Thanks