Ain't no magic number or symbols, well except for pyramids. When a carb has a pyramid shaped transfer slot, it has the great power of the bubba.
For a model 4150/60 family, older Holley's should have .020 to .040" showing on the primary slots at idle.
If the slots were made wider, or longer (common these days) then there is more area...
IIRC this is a pair of 1:1 carbs on a tunnel ram. So at minimum that twice the fueling at idle than a single 4 bbl on the same engine.
I don't recall - or maybe we didn't know how the secondary idle is fed. If its through a 'snake' passage in the throttle plate, or independent...
Map out everything that is accessible. Idle Air Bleeds, Idle Feed Restrictions (if not buried in the metering block's idle up passage, etc.
