If you are running front discs/rear drum there is a good chance you will have excess rear bias.

I'd keep the original drum brake setup... which is basically a "T" for the front and add a rear proportioning valve. The Wilwood valve is a good one. It can install neatly on the drivers side inside frame rail where the rear line runs.

If you are running a new master, it may not have a residual pressure valve for the rear brakes. A residual pressure valve can be added in the same spot you add the rear prop valve. Many consider this valve optional but Inline Tube, where I got most of my stuff, recommends it.