At least, as I recall, the disc on the side of the hitachi carb should be a vacuum advance. And the line that feeds it, has no vacuum at all. While messing with the wiper motor, I decided to grab my vacuum gauge and hook it up. Just so happens I pulled the line to the distributor, and got a big fat 0.

 

Am I correct, that this is the vacuum advance? And can I just find a good vacuum line, and T into it to put vacuum back on the distributor?

The vacuum line that connects to the distributor should connect to the carburetor at the other end. At the carburetor, the connection should be upstream of the throttle plates. At idle you should have about zero vacuum and the vacuum should increase as you open the throttle.