73 Duster Brakes do not work

Welcome aboard. No one has responded yet, so I will give it a stab. First, a picture is worth a thousand words...
From the description given of the "valve", it sounds like the brake line "tee". Hose comes in, and the tee splits the fluid to the two sides. The knob is probably just the bolt that holds it in place.
Now, why don't your brakes work? You will need to give us some more info. Do you have any pedal or does it simply push all the way to the floor? Are any of the brakes working, front or rear? Have you checked the fluid level in the master cylinder? Have you bled the brakes? Have you replaced any parts in the brake system?
As for the 8 3/4 original to the car? Probably not.
Bring us more info and we'll try to steer you in the direction to start.
C