..with a large cam and lo manifold vac at idle, a mopar can will not advance properly and will just dither in and out and give an unstable idle.
..a replacement can that starts advancing at 2 or 3" below the idle vacuum is required.
.. this will give more advance at idle,a cooler more complete
burn,and probably no overheating at the stop lights.
..by running ported vacuum you are probably leaving a little on the table.