I found this article online.Seems to describe brake pretty well.
The thing that doesn't make sense is that our cars did not come with a proportioning or metering valve. (not that I know of, I currently don't have one, but that doesn't mean there wasn't one from the factory)
I had a '71 Scout II some years back. It had drum/drum with dual piston master cylinder. It had a distribution block with a switch from factory. The block's purpose is to activate a warning light if there is a failure in the braking system.