Holley Idle Screws Not Responsive

Not enough initial... try 16-20 range and start over at the baseline carb settings, like what redfastback has in his set up. You're likely already on the transition circuit at idle, primary throttle plates too far open. More initial will allow you to close up the primary blades.

JMO, Leave the drill bits alone until you exhaust EVERY other possible solution.

Make sure the float level is proper and all the vacuum ports are either connected properly or blocked off.