To tell you the truth I'm not sure about the master cylinder and would have to ask the shop for a true answer. The car was already equipped with 6-pot calipers so it may be fine. Also, the car has an adjustable proportioning valve located right by the driver's right knee inside the cockpit so once it's back on the road we should be able to dial the braking in very nicely. At the wheels the change to carbon required new spindles as well as the rotors, calipers, and pads.
One thing we've recently decided to add to the mix is traction control. The car should weigh under 2,000 lbs. and with the power we expect to send to the rear wheels we feel it's prudent to let the computer assist in maintaining traction under strong acceleration.