I am in the process of rebuilding an 03 Ultra 150 that had a bad PTO Cylinder. Upon opening, it looked like an oil seize on that Cyl. I took the motor down and found that 2 of the cylinders were sleeved. I wanted to return it to stock, so I got 2 new/slightly used ones. I also got a couple of stock STD pistons to replace the sleeved cylinders. Now I am noticing a stamping on the cylinder right below the head towards the exhaust port. Two of them are stamped 'B' the other one is stamped 'C'. Do I need to worry about this? I have a bore guage, so I am going to check all of this before I put them in for good.

Please let me know if I am missing something.