what master cylinder for disk/disk set up?

Or you could not use any factory based proportioning. Run a 2-way splitter in the front and run an adustable prop valve for the rear. Even if you use a factory drum prop valve you will likely need to adjust your rear line pressure some because your setup is vastly different than anything that mopar produced way back when. Remember everything affects how the brakes work including ride height, tire selection, and vehicle weight. All of these factors will be different from factory.