guess is the wrong master (piston diam.) See the MPB site below as it's about the best on the 'Web. Click on the tech section and review the FAQ's and Troubleshooting guides. Mismatched master bore size and/or pedal ratio when switching from drums or OEM discs to aftermarket or other discs is usally the culprit. A adjustable prop. valve is often a good idea to balance the braking system (later) but...if the car won't stop now....it won't do you much good.
http://www.mpbrakes.com/technical-support/troubleshooting.cfm
