Vaccume advance

The big problem here is that you will have vacuum there all the time, so you will be permanently advanced... I've been looking at the same thing, since I have accuspark distributor I might buy one of their black boxes to electronically control the advance.

If you hook up direct to manifold you will have full vac advance at idle. This is not necessarily a bad thing. The problem is that the massive changes as you open the throttle can cause wildly varying timing. This can cause stumbles and hesitation if not correct. This normally requires reworking the mechanical advance curve also to suit.

Full ported vacuum can be desire able on a low compression motor.

spigot

Robmk2
The big problem here is that you will have vacuum there all the time, so you will be permanently advanced... I've been looking at the same thing, since I have accuspark distributor I might buy one of their black boxes to electronically control the advance.

Wrong, the only difference between timed and ported vacuum is that timed comes on once you crack the throttle open. The signal is taken from just above the throttle plate. The amount of vacuum at all revs and loads is exactly the same between the two once the throttle is slightly opened up.

Wrong,
Inlet manifold vacuum / manifold vacuum is any vacuum connection below throttle plate.
Spark port vacuum / ported vacuum is connection on carby just above throttle plate.(specifically designed for distributor vacuum advance purpose)

You are correct that ported vacuum is taken just above the throttle plate, but the ported vacuum
Is also affected by the air speed through the carby and around the throttle plate .

Cheers