Holley/Demon Carb stumble

PRH said

The best luck I had with building a carb from readily available parts was the original Proform HP 750 body, using stock Holley 4779 metering blocks and a plain Jane 4779 type baseplate.
I built a few of those, and they required minimal tuning to get dialed in.

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I've also found this, my best carb is an older ProForm main body with a 650 doublepumper baseplate using a pair of metering blocks off a couple of 4412 500cmp 2bbl carbs.
Primary metering blocks off the 3310 750 vacuum sec are my favorite as they have the same calibration and can be found for cheap on Ebay.