The piston crowns will take a fair few miles before they become encrusted with carbon once more :) ( Assuming ideal engine operating conditions are met )

Longer if you polish them ;) ..............Don't polish the direction arrows from the top of the crowns though :eek:

John I think would not charge you and if you are buying from him he is going to advise what is needed ie regrind or what ever,it is possible to put oversize rings in but not a diy for the fainthearted.He is the one I would trust to check it and supply bits. There is also Northern Rebore (Ronnie) in Elswick Road Ncle.