Next you need to understand how the idle speed screws affect the transfer slots. If the throttle plates expose too much of the slot then the amount of fuel that will flow at idle is affected. If the plates are over open enough at idle then enough air will flow through the Venturi boosters to start flowing unwanted fuel from the main circuit. There are many posts on here that explain these issues well.

Ignition timing is critical. It bears repeating, Ignition timing is critical. If you are setting it to some smog spec it will not run properly. Your distributor may/will need to be modified so that you can have enough initial timing without having too much total timing.

Powervalves are often misunderstood. Pv's add power enrichment, never idle enrichment. Even some of Holley's literature is incorrect. Powervalves add fuel to the main jet circuit. No fuel feeds through the pv until there is enough airflow through the venturies to start fuel flow through the main jets AND the vacuum is low enough to open the pv. No matter what vacuum number is on the side of the valve it does not add fuel to the idle circuit no matter how low the idle vacuum gets. You could put in a pv that opens at twice your idle vacuum(not recommending that) and it will always be open but it still will NOT flow extra fuel at idle.
If you can screw the idle mi xture screws all the way in without stalling the engine then the powervalve diaphragm is likely blown and dumping fuel directly into the vacuum passage from the manifold.