Brake Master Cylinder Valves

I have a brake master cylinder off of a '74 Dodge Dart Sport, diameter 15/16. I would like to use this with my disc brake front conversion. The conversion is off of a '74 Duster. I was told I could use this master cylinder but that I needed to take off a valve. Does anyone know what valve, where it's at, and how I take it off? Or does anyone have a recommendation for a master cylinder I can use?

:violent1: