Master cylinders..manual vs. power?

I have MANUAL Kelsey hayes brakes on my 1972 dart i just installed. I see most people like the 15/16 bore MC for manual discs..well, looking at my local oreilly, all the master cylinders for manual brakes are 1.032 inch..in order to get a 1 inch bore MC i have to get one for POWER disc/drum brakes..is that ok to do or do i have to have one that is strictly for manual brakes? I would like to pick one up tomorrow..