You cant just bore the stock cylinder even the small amount anyway as you either need to have it replated after or sleeved. You also need to be able to buy a piston & gaskets to fit the new bore size.

 

You can bore the stock 250 cylinder out to the 331 & still have a good cylinder wall margin & still be plated. The sleeve that I install for the 331 kit is the same outside diameter as the stock cylinder.There is a wet sleeve that can be installed that is a little bigger LA Sleeve said they made it for a special application & havent sold that many of them..
Bill