Except for the balance passage (visible as a small hole in the cross-over webbing) the carburetors are semi-IR like the original Corvette. This requires idling on all 3.
Typically the center carburetor feeding cylinders 3 & 4 needs slightly richer jetting due to the difference in firing intervals between its 360-360 and the end pairs 240-480 intervals (as Jaguar detected 60 years ago).
If those are common 2G carbs, they are simultaneous operation and will have all 6 throats open @ WOT.
Yes, this is considerably larger than he Corvette YHs but the needs of a pair of cylinders are not 1/3 of an engine unless there is a substantial plenum.
Anyone considering using 3 X 2G: although these were rated at 3" Hg I doubt it will pull that much. This means the high speed mixture will lean out as RPM rises, requiring a HSAB reduction (not just a larger main jet).
