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

And to those who depend on Chrysler to have " done it right", then why are we modding our cars at all?
-All our muscle cars would have had; way more power,more gears,bigger brakes,WAY more caster, stiffer Uni-bodies,factory exhaust headers,etc.
-Our cars would never have had 9 inch brakes,front drum brakes,7.25 diffs, open diffs,that lousy over-assisted P/S box,13inch tires,E70-14s on the back of any 340 car, etc.
-There was no "right"'rule book,back then. They were in the process of writing it. If they didnt have a rule-book, how could they know the "right way"?They did pretty good for the time. And they invented all kinds of stuff to put on different car lines that we can,today,pirate, to help make our cars,"right". Subjectively right that is.
-If they would have "done it right", I would have saved myself many thousands of dollars and hundreds of hours of work.
-Just my 2cents.