"A" is a rather large, rusty proportioning valve, it appears to have an adjusting knob on the bottom. Unfortunately, it is plumbed into the front brake circuit instead of the rear brake circuit.
B is the pressure differential valve, aka the shuttle valve. It detects a difference in pressure between the front & rear brake circuits and illuminates an alarm light (wires should be hooked to the middle post on the firewall side, but I don't see any). The gizmo with wires on the left hand side is the brake light switch.
cowboy from hell
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