Mattax said

I don't recognize the valve either, but I'm most familiar with the earlier fixed caliper systems.
Would the previous owner know? If you have some additional photos, maybe someone will recognize it. Might also look at Master Power Brake, SSBC and other aftermarket places.

If the PO doesn't know, and there is no markings, knowing where the connections from the m/c go, and what lines go in and out of that valve we can figure out what is going on.

My suggestion is to make a simple drawing of where the tubing from the cylinder goes, noting all the junctions and devices on the way to each brake. That's just me, I can understand things better with diagrams.

To learn about the braking hydraulics, the 1967 pamphlet is good start. In this they introduce the tandem master cylinders. All routing from then on is just minor variations on that. (for chrysler and most american cars that is). The newer booklets I linked to assumed that background was familiar.
1967 Imperial & Chrysler Dual Hydraulic Brake Repair Book - Session 232

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