Still haven't figured out the idle issue...

IMO....while the primaries feed the idle wells in Holley's, that would be the last thing I would work on. My order would be:
- Float settings right
- Timing changes to see if that helps
- Secondary stop adjustments and a couple of iterations
- Small float setting increases
- Accelerator pump
- Primary jets

BTW, OP, do you still have the points in the distributor? Make sure the peak points gap is around .018" and that the 'nubs' on the distributor shaft that operate the points are not worn down. A dwell meter would be ideal to check points operation.

The reason to look at the ignition system a bit more is that the energy required to make a spark jump the plug gap will vary considerably with load, exact A/F mixture, and operating phase of the carb. You might find it very good to do an HEI conversion.

And as 3spd6 said, what else is on/in this engine?