What kind of Idle are you running at stop signs?

Yes, because it is BS. Swapping to a 4bbl on an otherwise-stock Slant motor is a big and ongoing waste of time, money, effort, knuckle-blood, and gasoline, and it damn sure doesn't "smooth out the idle". If your idle isn't smooth, it's because something's the matter. See tune-up parts and technique suggestions in this thread.
What is the venturi size and throttle blade size of the 1 & 2 bbl. carbs?

There sizes against a small 4bbl. like a 390 or 450/465?

I'm not so sure I'd call B.S. so fast.