And what you have marked as the Brake switch is the metering valve. Under the first 10-15 lbs of pressure it should move.

I think he's right about the front lines too, Dr side on top & pass-side on bottom.

Brake switch on top ..correct.

Rearmost port to the rear brakes.

The boss on the bottom near the rear port is the actual proportioning for the rears.

Technically the factory called this a combination valve since it incorporated the proportioning & metering valves of earlier years when they were separate pieces.

Butch