A metering block vacuum port is generally ported vacuum, and wouldn't affect idle speed, although you don't want it leaking
That being said, if the primaries are too far open, it would come alive and likely raise idle.
I'd email Drew, but what I would likely do for info for him is see if that port is alive at idle, if it is, look to see if there is anything binding, like a base plate gasket, etc, or another vacuum port leaking, PCV, etc
If not, close the primaries a little on each carb, see if it drops back
If it doesn't put them back to where they were, close the secondaries a 1/4 turn from the bottom and see what it does