Entirely different. It's a metering valve. Not used on a-body's. If you flip to the next page, you'll see the check list of what goes with which brake system. I did say it could be confusing!
Metering valves were used to hold off brake pressure on the front lines when the pedal is first applied. This was reduce the chance of front lock up on very slick surfaces such as ice. As the car begins to slow the weight transfers foward and the tires will bite better as the front brakes get their full pressure.
