Disc / Drum proportioning valve / distribution block. If this is the case you will need to tap the stud out of the bracket that is included on the valve. If you don't have the stud on the car you can use the one provided on the valve bracket.
Mopar Disc Brake Proportioning Valve & Metering Valve for Disc Drum A,B,C & E
Universal Black GM Disc Disc Brake Proportioning Combination Valve 4 Wheel Disc
Disc Disc Brake Proportioning Valve 9/16" 1/2" Lines & Bracket PV2 Combination
Chrome Disc Disc Brake Proportioning Valve 9/16 1/2 Lines + Bracket impala nova
Disc brake proportioning valve 4 wheel disc pv4 mounts below GM master cylinder