[jwd]

There have been countless articles written on this subject by many very knowledgable people and the bottom line is, use manifold vacuum. Ported advance is a result of pollution control. Manifold vacuum is what ALL manufacturers used prior to that (1971). It works much better and your engine will run cooler at an idle because of having more advance. The ONLY difference between the two is at idle. As soon as you open the throttle, they both work the same. To eliminate the hunting, get a unit that gives you full advance at 2" of vacuum less than what your car idles at. Most aftermarket dist. (MSD etc.) use GM advance units. I have a list of all of them and they are all available at any parts store for about $7.00.