What if I don't change my Master Cylinder on a disc conversion?

And to CJP;
-I have the KH 4-piston/10x2.5 system,with the really small booster on my S-clone, street 360. I have 235s up front and 295s out back.DOT5 silicon fluid and a gutted P-valve.On the street,I have never wished for better brakes.They have even pulled me down hard from 93mph (car goes 93 in the 1/8th), several times in a row, without fade or drama. This system came off a 70 Duster with the Rallaye Suspension option.
-If you have a similar system, on an A-body,and for street,and its not stopping "as well as expected",I surmise that it may not be working correctly.
-If youd like to start another thread,perhaps we can help you work it out.