what master cylinder for disk/disk set up?

You wrote that you intend to get a master cylinder from a disc/disc vehicle. Thats NOT what I did. My M/C may have an OEM connection, but I'm not sure of what it is. I ordered mine through Dr Diff. The important thing is the BORE size. It is crucial in non power applications. It needs to be either 7/8" or 15/16" to have a decent feel along with the proper pressure at each corner.
The reason for NOT using a disc/drum prop valve? Those are designed to limit the line pressure to the rear drums, while giving full pressure to the front brakes. Using one of these in a 4 wheel disc system will result in low pressure at the rear calipers and poor performance. A 4 wheel drum combination valve works in an approximate 60/40 front to rear ratio.