I'm not sure but I think it is just a junction not an actual valve. On my 78 and 79 axles it is positioned just like yours. On my 74 axle it is rotated 90 degrees. All three work.
Proportioning valve would be on the booster. Mounted on the lower mounting bolts.
I think your T is is installed incorrectly. It appears 180* off and upside down. Look at the link go to post #124 and scroll down to the pic. 2 of the ports should have female inverted flares in them so the hard line flares have something to seal up against. I think the soft line port would be open and tightens up against the T with a copper sealing washer.