Ported vacuum is manifold vacuum but its just a port above the throttle plate so it don't come on until you step on the gas. It will still drop to about 0 vacuum at WOT. I agree with most that so much depends on the combo. Working as a tech from 1974 up to 2011 most of the older dist cars I worked with seemed to use ported vacuum for the dist but I did see them both ways from the factory as some used full vacuum at idle. Myself I don't use ported or manifold vacuum on my 63 and that's because I got a great deal on a Mallory race dist and I use it and it has no vacuum advance on it. I have it set up with about 24 degrees at idle and the rest of the timing set up to come in fast. I have my full total mech advance in by 1800 to 2000 rpm. The car runs great like that for me. If I had a vacuum advance on my dist I would have tried it to see how the car likes it since mine is mostly a street car. But I will say it runs good with the quick mechanical advance I run. Ron