What kind of Master Cylinder would I use? 4 wheel disc

Right.. It seems to me if I remember correctly, everyone seems to be using stock style MC's on this board. Just a quick look in the Summit catelog doesn't note 4 wheel disc or 2 disk/2 drum.

I think the internal thing may be a residual valve. It keeps a certain amount of preassure in the line for drum brakes. Disc brakes don't require them, or require one with a lot less preassure, it's one of the two. I haven't figured that out yet. I am not sure if these are build into the MC or if they are in line of the brake line. I see them for sale in Summit that just go in line of the brake line.