mine had A/C i think i have a pic of the firewall but without the valve.it is a square hole next to the blower mount[circle hole]
edit:" i am sorry you asked for the valve placement not the hookup on the fire wall.
from what i remember the vac hose was 1 ft long from the firewall.
here is a pic as it was connected.sorry it may not be clear enough!
edit:as i am remembering my valve was activated by cable just inside the firewall 1 unit where the hoses connect in the engine bay and the cable inside the car.the vacuum line went to the intake for the vacuum lines inside the car for the divertor door for the a/c heat.i feel dumb after posting all this.maybe you hade a vacuum activated system.