Distributor Vacuum Advance?

The problem with that article is that that engineers were using ported vacuum long before they could spell emissions so it's certainly not something that was done to meet emissions requirements. Also, if you are relying on the vacuum advance to add additional timing to clean up the idle the second you touch the throttle it goes away and you are now in a situation you don't have enough timing (the rpm's aren't high enough to be adding enough mechical yet) for just off idle performance. This results in throttle tip in hesitation and general poor light throttle performance.

You are much better off setting the initial where it needs to be for a clean idle and off idle performance. Set the total to where it needs to be for max high rpm power. Then adjust the rate that it comes in so you do not have any mid rpm detonation issues. Then lastly add ported vacuum advance to add the additional timing needed for cruising. Doing this way also minimizes the interaction between the various settings making dialing it in much easier.

When they had to start meeting emissions requirements in the early 70' they quite often used a manifold vacuum connection but also had thermal switchs and/or gear position switches that controled when the vacuum advance worked.

I purchased a new AMC Hornet X in 73 and it had both. When the engine was cold you got no vacuum advance and when warm you only got vacuum advance when the tranny was in 3rd gear. It also had a dashpot that would control the rate that the throttle would close so if you blipped the throttle it would take a second or two to slow down to idle speed. The car never ran well until I removed all those contraptions and hook the advance to a ported connection.

My sister also purchased a Mercury Zephyer in lat 70's it had a vacuum advance with vacuum applied to both sides so it could advance and retard the timing. This was controlled by an electric module.