Scooterotica

Hi, I'm looking for some info/advice on what i need to do. Quite simply I want to build a touring engine for my ser. 1. I'm not sure of what chain/sprocket set up I need. I'm still gathering parts for this engine but so far this is what i have. A GP200 engine case,cover and maghousing. I bought these second hand and they had no gearbox endplate and i have since got both a GP and LI style endplate. I also have a brnad new GP Tameni crank, A stage 4 200 barrell and head, a 125 italian gearbox, a 47 tooth GP clutch basket, Electronic ignition kit, and a ser. 1 driveshaft, Plus most the other small bits, chain guides and levers, etc. I however don't have a chain or front sprocket, or kickstart shaft. I also have a 28 mikuni carb and old style WCLW exhaust, both of which I'm sure are really revvy. Though I do want to use an expansion type exhaust for the look of the scoot.
I have read that a 125 gearbox is close to a 200 depending on what sprocket set up is used. Nothing I have is concrete, like if the carb is too big I will go with something smaller, I have no piston so that is up for discussion, but i do insist on using an expansion chamber exhaust.

Any suggestions or advice is greatly appreciated and if I left any details out please just ask.