Correct Master Cylinder

First ,which auto parts are you dealing with and does the person know what you are talking about? I order complete master assemblys from the auto parts with no problem at all,and the parts are at the warehouse and are brought to me in a few hours and is a common part number.You should have tandem master cylinder which the 4 bolt hole pattern.if you can post a pic of what you have now on the car we can help you,Mrmopartech