Kelsey-Hayes proportioning valve for A body

Residual pressure valves are located in the master cylinder as required. Ie; 4 wheel drum master has a residual pressure valve each located in the port of the master right behind the brass line seat. A disc master has only one residual pressure valve located in rear segment port, you don’t want residual pressure on disc brakes.
the thing you circled is just and adapter to accommodate the brake line. You take the adapter out to get to the guts of the valve.

View attachment 1716063563
Thanks. I ask because I have two that are identical except for that adapter on top. The one that does not have it simply has the port for the line from the master cylinder to screw into with no adapter.