What year corvette is it that everyone seems to use the master cylinder from? The one with the cover that is round on both ends. I think it's in the '70s.
I believe 68-82 should all have the same master cylinder for 4 wheel disc brakes. Note sure on the bore size.
What V8 Bob said! Don't forget if you are mounting it under your car it will be "backwards", so the rear port goes to your fronts, and the front port will go to the rears. Don't ask me why it makes a difference but it does.