Leave the master cylinder alone (the only reason you would change over is to compensate for the different rod end on a manual versus a power brake system The Manual has a little dimple in the back , but the power brake has cup to hold the rod. There should be enough thread on the brake pedal rod to compensate for the difference in length (if not buy an aftermarket threaded adjustable brake pedal actuator rod).
The single eleven inch vacuum diaphragm should work just fine unless you have a lumpy, rough idling cam in your motor. The dual nine, or eight inch vacuum diaphragms are designed to accommodate tall deck big block engines with tall valve covers that eat up a lot of real estate under a hood and have ridiculous cams stuffed into the BBC motor such that it generates less than twelve inches of vacuum at idle.
Race cars use hand activated brakes that have a big spring to push the lever forward to quickly release the brakes and rely upon a parachute to drag the car back down from over two hundred miles per hour to eighty before you apply the brake lever again to slow the car down enough for the turn into the pit area. They don't use vacuum powered assist for their brakes so they can have as radical a cam as they want on a race car and not worry about street manners as they never drive on the street.