I am following up on this thread as the "last" thing on my punch list is this very same issue. When the vacuum line is removed from the advance, there is no miss or rough running when the engine speed is increased from idle. With the vacuum line installed, the engine goes into a noticeable shudder as I bring it off idle. Points, plugs, wires, condenser, rotor, cap are all new (not concours!). Problem existed before all of these components were replaced.
The vacuum advance mounting holes are oversized and the attaching bolts are undersized (not concours!). I noticed that the vacuum advance physically moves (with vacuum line installed) when I bring the engine up off idle. So the advance is working.
I am going to check the advance for its ability to hold a vacuum.
In addition to the items above, any other ideas?
PS. Application is NJ July 67 289 automatic, 2bbl, PS