It's a cast iron wonder with a gold-colored cylindrical part about the size of a Red Bull can. It bolts to the firewall just like the power brake booster. The master cylinder bolts to it, and it uses a regular M/C. There are two hydraulic lines, one is tee'd off the high pressure line out of the pump, the other goes back into the reservoir.

The core charge on one is $165.00, or at least it was when I replaced the one on my 1993 Suburban after around 200K miles. I bought a core on the 'bay for $35.00.
Bendix makes them, they're pretty much all the same.

They have been used OEM on mustangs, Diesel trucks and heavy duty gas trucks.

I love the smooth, even brake application. It's easy to modulate.

Do a Websearch, there'll be thousands of hits.

R.