Thanks for the report. Good to eliminate leaks in manifold or vacuum caps as possible problem areas.
If need to verify which cylinders are firing, may spray water onto exhaust pipes while engine running and watch for sizzle. Will assume you're correct about #1 and #2 cylinders not firing unless "choked".
So it seems that float bowl overflow on #4 carb is not preventing firing on #4 cylinder, and #3 seems to be firing okay and without any carb overflow. But even with the overflow situation on #1 carb, the #1 cylinder is receiving insufficient fuel mixture unless choked, and same for #2 but without the overflow condition.
From current symptoms, #3 and #4 are running okay (except for the pesky #4 carb overflow).
#1 and #2 seem to suffer most from "too lean" fuel mixture symptoms (and #1 carb overflow).
Will hazzard a preliminary diagnosis
Blockage in primary fuel supply circuits carbs #1 and #2 (failure of fuel passing from the float bowl through the pilot jet and on through the passageway to where it meets the pilot air screw tip at the small orifice in the carb throat (located just before entering the intake manifold) where fuel mixture is provided during idle and low rpm running (before the throttle slide and needle are raised). Cleaning and clearing the pilot fuel circuit requires carb removal and disassembly. Was hoping for something more simple.
And another guess as to the overflowing. Grit or crud in the float needle/seat area preventing closure and thereby allowing entry of excess fuel which escapes through the overflow spigots.
But the overflow might just be from a "sticking" float or float needle sticking in the seat. Sometimes the time honored method of tapping on the float bowl will free a stuck float or float needle and stop the overflow. (Okay to tap "pretty hard" but not Godzilla style).
And a final guess regarding float level. They could very well be perfectly okay. But the service fuel level should be checked (use the clear plastic tube method) before removing the carbs from the engine. However, the overflow must be first corrected in order to perform a valid service fuel level test.