cobbled brake system

Ok, I have rebuilt/replaced entire a body brake systems. no sweat. This one on my newest car (69 cuda), is very different.
I have not even had the car on stands yet but wonder what is going on with the assembly and maybe some guru here can tell me if its either Junk or jewels.
Prior owner told me this. C body front brakes, jeep wagoneer calipers on back. (8.75) dual disc master of some type. Unknown prop valve type. He never mentioned the adjustable valve in the brake line going to the rear which seems to do nothing. car stops "ok". Power brakes, pedal bleeds down fast to floor, red brake light comes on. fluid ok, haven't tried to bleed. doesn't seem to be a vacuum leak. engine stays at around 13". Prior owner told me it was an alternator light..lol..I can/t wait to tear into it this winter. but having fun driving this one.

Anyone seen these kind of mods? I have a new prop valve from another project just sitting here. and wondering if I should just remove the adjustable valve.