Here's the disc setup on my red '66 GS.
The original distribution block is still used for the two front brake lines.
The line for the front brakes runs from the master, thru the combo valve, thru the line-lock, and into the dist block.
The original inlet on top is plugged, and the new inlet is at the rear.
The rear brake line exits the new combo valve at the right (hidden behind the z-bar). I had to cut the old rear brake line and reflare the end.
I make my own brake lines..... NAPA sells a whole roll of line for about $25. Fittings were purchased from 'The Right Stuff'.