Hi Moby Mick
Suzuki recomond a maximum wear of .10mm (.004") between the standard piston and bore which is 58mm and from standard the piston clearance to the bore is .042 to .055mm (.0017" to .0023") which is measured from the bottom 25mm of the piston and 110mm down in the bore using a bore gauge, anything over this Suzuki recomend reboring to the next piston size which is .25mm (.010") oversize.
In answer to your question 1 is yes these engines have been successfully been bored out and they get machined on a small engine boring machine as changing the sleeve would be difficult because you really have no way of pressing it out from the top through the bottom because of the one piece casting of the block.
In answer to question 2 if you had any more than .25mm (.010") wear in the bore and you could fit the oversize piston in the bore then I would be throwing out the block because I would say it is well past it's used by date, if you could put a oversize piston down the bore then it will not be running true and would probably cause some serious damage to the piston and the bore.
Ther are a few small engine reborers around and even some of the Go Kart shops do rebores for small engines.
I hope that is of any help to you. Steve
