I would look at the airgap between the sensor and the black rotating part. They on their website claim the normal gap at .040" and looser than any I've ever seen, that's just plain crazy. WAY too loose, I've seen other more expensive sensors read erratically and nowhere near that loose. If distributor bushings were changed then set gap at say .015" with the distributor shaft pushed one way to minimize that gap. The looser that gap is, the less consistent the blips the sensor sees are, too loose and it begins to miss some of them from being too weak and your misfire. I run that close on every electronic unit I get my hands on, regardless of brand. You just have to make sure the two parts cannot touch, which would result in destruction of them both.
Basic electronic ignition tune-up trick on every one out there......... .............r un that gap CLOSE. Whatever is used in there to switch, either magnetic coil or hall transistor, works much more consistently with closer airgap.
Too loose may be why the tach went crazy, it could not read all the impulses there. Could as well be why when vac advance moves plate it quits running right. The vacuum plate must be stable as well.