Cylindrical shaped brass valve, some times called the pressure control valve or 'cigar' valve. Starting in 1968, disc brake cars have it mounted almost directly on the Pressure Differential Valve on the driver side fender apron. The pressure differential valve is also commonly called the 'brake distribution block'. We also sell our brake distribution blocks complete with the proportioning valves. The C8OA numbered proportioning valve started way late for the 1968 model year. We almost never have them in stock. The C7OA-2B091-C, numbered valve was used at the start and went well past March before the C8OA numbered valve appeared.
Ford part # C7OZ-2B091-B, casting # C7OA-2B091-C.
Here’s a video to help you rebuild the proportioning valve so that you can corral your Cat or Pony without fearing for your life.