[wolf k]

I think we all agree that vacuum advance is a good thing for street driven cars. The question is whether the source of vacuum should be manifold source or ported source at the carburetor.
The only difference between the two, is that manifold source would give you vacuum advance at idle, ported source gives you the same manifold vacuum, but only once the throttle is cracked open. Trace out the the ported vacuum port in a carburetor and you will see that it leads to a small hole just above the throttle blade. You will have the same vacuum signal with manifold source or ported source with any throttle position above idle.
So the the only difference between the two is, do you want vacuum advance at idle or not. The choice is yours, depends on what your engine runs better with. Generally, if you run with manifold source, then you will have to back out your idle screw further out to get the same idle speed, this may be a good thing or bad, depends on your setup.
I have heard some drawbacks with manifold source, is that it puts higher load on your starter because you are getting advance at cranking speed. I do not buy this, because we all start our carburetor engines with the throttle cracked, thereby, exposing the ported source.
If you have run-on issues with your engine after shutting off the ignition, manifold source may help you because your throttle blades will be more closed off at idle. Manifold source may also help those lumpy cammed engines idle better.
Again, there is no right or wrong source, it is what ever works better for your setup.