if i were you and wanted to changed those cylinders there are 2 options: 1 you can call vitos get there steel sleeves for the 10mm cyls have them installed and port them how you like, likely be able to start at 66mm bore so you have until 68.25 on blaster pistons. 2 send them to millenium have them strip the nicasil off and weld the tops of the ports, you port them how you like and send them back for plating. ive personally done both ways with the same set of cylinders.