It will tell you 2 things, (1.) that the front port is the one you should use,(2) that the diaphragm is good. Because, one port is for advance and the other port is retard, you don't want the retard side.
YOU COULD ALSO REPLACE THE DUAL WITH A SINGLE FROM YOUR LOCAL PARTS STORE!
Neither of you really need a dual port, unless you are going the all original route for show!I've been watching this thread as I stated in an earlier post that I just got my vacuum lines correctly attached. Interesting in that I have a manual and should have a dual port and only have a SINGLE. Is this easy enough to get from NAPA? I would like to get the correct one if possible. Thoughts would be appreciated. Thanks.