John, do you have a picture of the "T"? The best I can figure is the "T" would be in the 1/8" supply line going from the LARGE oblong canister to the AC controls, but is that correct? Wouldn't that be sized strange? 1/8" line stepped UP to 1/4"?
Yes I do. Please see the pics below.
As far as the size changes, I don't see that as a big deal, as long as there is enough energy available to get the job done. And there is with the design.
The tilt solenoid valve was shared with the Thunderbird, which as a luxury vehicle had a plethora of vacuum operated devices. The valve was not designed specifically for the Mustang. It could be (read: speculation) that the T-Bird had a larger (1/4") vacuum distribution backbone, and the tilt solenoid valve was designed to fit well there, and the carry across required some low cost adeptation.
As for location of the tee, you should be able to tell by the length of the hose that it was inside the pass compartment.