Modification to a 4 drum master cylinder for use on 4 wheel discsv. ?

Unless I missed it, an important piece of info has not been mentioned.
[1] Disc brakes require about 50% more line pressure than drum brakes.
[2] With drum/drum brakes, car makers 'proportioned' the extra braking force to the front wheels by juggling the wheel cyl size.
[3] With disc/drum, the proportioning of the line pressure was done by a ....proportioning valve. Not normally fitted to drum/drum cars. But needed with disc/drum.