Hi Danny, all of the associated parts lists
at the time that came with the owners operators manual only went to three sizes over for some reason. They always latter added larger size options as bulletin releases, for some strange reason
Don't worry about it. You can get pistons now all the way up 2.5mm sleeve savers, Although I have had a cracked 250 sleeve, it is
very rare for a 250 sleeve to crack.
Call Les for a 68mm woosner for the 67.75 bore cylinder that you have. He is now got them down to $149.95. Your engine will be a little snappier too. Their reciprocating mass is a lot less than original Malhe choice.
A Woosner is teflon coated. I like to bore them neat and take it easy for the first three hours. And as usual make sure you chamfer your ring leadins on your ports and set your ring end gap. Machinists are only paid for boring and honing, so that is all they do.