Just so we're all on the same page, the drum brake cars used a distribution block only. This is simply a tee fitting with a differential pressure switch that illuminates the BRAKE light on the dash if you lose pressure in one half of the system.
The 1967-70 disk brake cars used the hold-off/metering valve in addition to the distribution block. This is the same distribution block used on the drum brake cars.
The 1971-up disk brake cars combined the distribution/metering/proportioning functions into a single, cleverly-named combination valve. The brass item you have is one of these post-71 combo valves. As noted, it replaces all other valves and distribution blocks in the system.