Mattax has good advice. B/E Body disc for 70 used a 1 1/8" Bore MC with power assist. Extra volume needed for the disc. As stated, the residual valve is removed for the front disc section of MC. Leave rear in for the rear drums. If you match the 70 service manual set up you will be happy. Certainly if you want more modern performance oriented, an after market system may better suit your needs, but I am happy with the 70 set up on my B body and it brakes fine. Just a cruise car.