Master cylinder for manual disc brakes?

I ordered one from rockauto.com for a '72 Duster with disc brakes because it has a 15/16" bore for less pedal effort in my manual brake car. It bolts right in. While the smaller bore required less pedal effort it does have longer pedal travel. The books all call for an over 1" bore master cylinder for my manual disc brake car which requires a tremedous amount of pedal effort.