How much RPM drop from park to drive with stock type 340 convertor

Mix of terminology...
I knew what the Transfer Slot is but how does the word 'sync' apply ?
Isn't the transfer slot part of the 'off idle' circuit and feed air from the 'air bleeds' ?

I also know with a '4 speed cam' you don't need to drill the primary butterfly... but .. when do you need to drill that 'bleed hole'?
Can only assume it is needed with long duration 'full race' cams.

I'm running a 340, loose convertor, with 484 Hyd Purple (3/4 race ..lol) and a Holley 750 DP 2 port idle adjust ... and don't have or seem to need the drilled butterflies.

So when do you need to drill the butterflies ?
Can't the original poster also use a vacuum gauge to see if it drops off too much when dropping it in gear which then disrupts the idle fuel/air mixture. ?