I have a Corvette master cylinder in my 65. I put it in a while back and now that I am converting to front disc rear drum, I read that these are great master cylinders for the swap but make sure you have a 1 inch bore and not a 1.125 bore... I do not remember what my bore size was when purchased... Honestly I didn't even know there was a different option available...So how do you know the difference? Is there any way to tell without unbolting the MC?