HEI Vacuum Advance

[RichardJ]

The drawing that mr48chevy posted is a "Closed PCV System". With a valve cover breather, you have an "Open System".
The arrows shown in the drawing posted above, show the direction of air flow when you have high to medium vacuum levels.
When accelerating and especially at WOT, vacuum levels are very low and at the same time, blow-by past the rings is at its highest. During this period, the arrow in the hose, valvecover-to-air cleaner would be pointed toward the air cleaner. Blow-by is still going into the engine to be burned, just not as much through the PCV Valve.
Image when under heavy acceleration or WOT is below.

I don't want to restart an argument about manifold vs ported vacuum, but I attribute your improved performance and drivability to the fact that you previously had no vacuum advance at all. You had mechanical advance alone.
Your Edelbrock carb is a newer version of the Carter AFB, they started making in 1957 for Olds and Cad engines.
The Carter AFB did not have a small manifold vacuum port on the front of the carb. They also made the Carter AVS for '67-71 Mopar engines and a '66 Chevy 327. One year only AVS on the 327 ?

I'm using a Carter AVS from a '71 383 mopar on my 292. No small manifold vacuum port. Runs great on ported vacuum. My 292 originally had a Rochester B. No manifold vacuum port and it ran fine with the ported vacuum port. Chevy used the same Rochester B all the way back to about 1950 and with ported vacuum. No manifold vacuum port.
Chrysler also used two Carter AFB's on the 426 HEMI. They were not fitted with manifold vacuum ports in the casting either. One carb had a nipple for ported vacuum and the other carb had the ported vacuum port capped.
Some of those Carter AFB and AVS had a small manifold vacuum port on the pass side that was used for a choke pull off, depending on the style choke. No manifold port provided for vacuum advance.