Dual quad info

I started with Summit twin Holley 390 dual quad package, that's just the carbs.

Needed to also get the Holley Vacuum Secondary Carburetor Accessories 20-73, as well as an air cleaner setup.

Then went to 600s, bought used and rebuilt. Far cheaper than the 390s and a huge difference.

Always had 1:1 linkage. Although the tr has a crossover built in, never used progressive.

Not sure how a regular dual quad intake works, whether each carb feeds all or 4 cylinders.
Either way, is there a potential for some to run richer/leaner with progressive?

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