Divorced Hydravac setup

Ok, I'm stumped. I've heard of there being a divorced vacuum boost assembly that was available as an option for early Jeeps with the "through-the-floor" pedals, but for the life of me I can't understand how the darned thing works. I'm familiar with the firewall-mounted units and how they work, but I just can't get it into my thick head how a remotely-mounted unit does the job. Cananyone shed some light on this?

 

IIRC the frame mounted master cylinder pushes brake fluid to another cylinder on the booster, which in turn boosts the fluid pressure to the wheel cylinders. My first CJ5 had one, been many years but I know the master cylinder was in the original place on the frame. Worked pretty good most of the time.

 

Ok, that makes sense. I just saw one for sale and I started thinking about snagging it for the flattie, but I really don' thave the time or the money at the moment. What was I thinking??