"No feedback brakes" go from nothing to full lock

OK, I will first make sure the push rod is making contact when I move the pedal. Then I will make sure that there isn't a vacuum leak anywhere else. If no luck, then I will remove the booster and go manual brakes. What size piston bore do I need in the master cylinder for manual brakes. Anybody got a part number for Dorman, O'Reilly, or Auto Zone?