Filling Throttle Plate Holes
Before I did anything with the holes, I'd verify where the blades are relative to the transition slots. You only want .030-.040 showing. With that cam, I've never been able to not have holes in the butterflies.
That's why most of the new carbs have a built in, adjustable air bleed system. It presents a controlled air leak so you can get your idle speed up and the throttle closed like it should be.
But there is nothing wrong with the hole. I think you still need them.
I agree.
Set the throttles by t-slot.
Count the turns of the idle speed screw to get .020, .030 and .040" showing.
Write that down.
Next with engine warmed up, do some iterative testing to find the strongest combination at a reasonably slow idle speed.
Adjust the throttle like YR just said, no more than .030-.040, but at least .020.
Use the initial timing to further adjust idle rpm.
After each adjustment of throttle position, check and adjust idle mixture screws.
If its an automatic transmission, putting it into D is a good check for power at idle. It should not significantly drop rpms or vacuum.
If you find the timing is moving around at the idle rpms,
then put more tension on the distributor's primary spring.
In other words, if its idling around 950 rpm and its at 20*, and then you lower the rpms (by placing it in gear or reducing throttle) and you observe the timing has dropped to 18* at 900. Maybe not a big deal if its just an in-gear test. You'll have to be the judge on that. But it is a big deal if your trying out a little less throttle at idle. In that case you want the timing the same as it was before, otherwise its not a fair comparison.
