My tuning skills have hit a wall.

[burnin oil]

My guess are the main air bleeds are different sizes. Try matching them to the Holley and see what happens. Next time you have the power valve out check and see if there is a removable brass plug with a hole in it. This is what's used to adjust the power valves flow rate. Vacuum just sets the opening and not the actual flow of the circuit. Demons are notoriously rich.