vacuum advance idle issue?

Well if the vacuum line is on the correct carb port, that is 'ported vacuum', which is taken out of the carb throat above the throttle plate. It is low at normal idle, and rises when you open the throttle. So the distributor advances with throttle opening from idle to mid-throttle.

If it idles OK with the hose plugged, then goes to heck with the hose connected, I would check for a leak in the diaphragm of the vacuum advance cannister. With the car idling and the port from the carb plugged, have a vacuum hose connected to the advance cannister and suck on it. If OK, you will hear a change in engine operation AND you won't be able to keep sucking air through the diaphragm.

Now, if the diaphragm is punctured, then I would not expect as much effect at idle, since the vacuum leak is above the throttle plate. But, if the carb is adjusted for some reason with the throttle plate a bit open, then a leak in the diaphragm would effect idle. And such a leak would certainly effect mild throttle openings. So, it might no be a leak, but that is a first check on the vacuum advance diaphragm.

Do you have a vacuum gauge? It would be good to have for this. OK, good deal on the timing marks and timing light. Just was not clear how you were doing this.

And the notes above on the valve lash is good. Can't help you on the video posting!