Drums to Disc

Hi all,

I have all the PST parts to rebuild my front end and am going to change it to the factory a-body Kelsey-Hayes disc brake setup I found off of a recently driven car from a junk yard. My question is this. I've heard when you do this you have to change the master cylinder as well. When I call the local auto parts stores, they only show one type of master cylinder available and it does not specify drum or disk. Napa shows a different part number for slant six cars versus v eight cars but thats about it. Does anyone know the correct master cylinder to buy? Part Number??? thanks