Ah, yes, I do that test often, carb cleaner around the #2 throttle shaft shows a slight drop in idle, but nothing more around the rest of the carbs or intake.

I really do not think this is the problem. I dealt with a poor intake seal once before and know the sound fairly well. High pitched hiss/whine - not getting that now.

I'm probably mis-remembering the vac gauge results. I was a bit thrown by the whole inch-pound thing on the gauge.

I only tested it on the vac-advance hose nipple on the forward car, not on the main intake manifold. I'd need to make some sort of connector to check there.

It might not be a bad idea for me to replace the carb to manifold gaskets just to be sure.

Still, I'm trying to determine if I made a false assumption about part-compatibility when I built these carbs. Nobody has jumped on my understanding of carb function, so I'm guessing I have a decent working understanding... The particulars are something else.