Grant Sport Piston in a stock PX200E 1993 km23012 , questions

Hi Community [:$]

I want to give the old lady a new heart and are looking at the Grand Sport Piston.

Question?

How to i messure what size i need (stock piaggio barrel) ?.

Any other things i should change while i got her opened up ?

The speedo says 23012km (14299miles) and the previous owner said he has never changed a thing inside the engine!

Please advise me

Best Regards

Kasper Winding

Denmark