I had both transfer slots adjusted to .020 when I installed it.
That is setting to basic ball park ...when one then istalls a carb dizzie what ever they then NEED to be dialed into THAT engine.
on idle circuits yes the carnb and dizzie have individual 'circuits.. like having separate carbs/dizzie for each job of
idle power and cruise...
so u start with 20/1000 set the idle avance to ball park also
on stock cam to mild street 8 to 12 , lumpy street 16/ 18/ wild cam that should be track upto 22 deg
Then adjust the carb idle circuits so the mixture is around 14.7 to mid 15s by changing the vaccuum 'leak' past the secondaries has the idle mixture screws and the idle speed screw are 1 1/2 turns out +/- 1/2 turn
If u cant get that either the carb is way to big for that engine.. which in this case very unlikely.....or there is a vaccuum leak somewhere....
And there is most proberly where your problem lays... worn butterfly bushers , and or incorrectly set bore to butterflies adjustment
I have an older model Holley 850 carburetor (0-9380).
It is not uncommon on old used BIG carbs to find the butterflies out of adjustment, due to someone playing with them , or someone having your issue, had the butterflies fully closed, car sits for a while, they jamb, bend a butterfly shaft , And wear the bushes...maybe even incorrect carb to base plate gasket.
It seems u know the basics and maybe more, of what u are doing .. checking timing marks ...setting slots etc...what should be happening isnt
I will lay odds the issue is an unwanted vaccuum leak, and most probably the old carb
Its that simple...
Then once u have established the idle circuit tuning specs u proceed to the power cicuits, get ball park AFRs 11.5 / 12.5 lock the cent set advance to 36, make runs and retard till sudden power drop.. couple degs above this now has your power circuits sorted... and your tuning specs set
Now just juggle/ adjust the cent degs , the VA degs and the VA vacuum range to meet the engine requirements
For get the drill hole crap, thats just a left over myth from way back in the 50s/ 60s when there was no or very little secondary adjustments..