It "LOOKS" like they just pulled the existing drum distribution valve out and used a union to join the lines. This eliminated your brake warning lamp switch. The line going into that added rear adjustable prop. valve appears to be the original line all twisted and rusty. Inline Tubes would be the place to start. Adding a 71-72 combination valve should take care of your warning light and the prop. valve need with a stock 71-72 type installation. They make these new along with the lines and brackets. A SS line kit should be no problem for them.
www.inlinetube.com