Dual quads versus big hammer!!!...

What was the idle speed for that idle vacuum??

Keep working with it.

It may be either getting on the mains too late or, you need to get the metering rods out of the jet quicker.

How to accomplish this with those carbs I can't say. But it can be done.

Well, you change the set up spring to get the metering rods up quicker.

If you can drive it, see what the vacuum is at a cruise. That would be interesting.