[MKS427]

Your rich at idle condition may not be rich at all if you have a big cam. Higher degrees of lobe separation cause raw fuel to get into the exhaust, so it may not actually be rich at idle, not in a menner that can be tuned away at the carb. I spent a long time chasing this before I found out it is not going to change.
As far as the vacuum secondaries go, a big cam affects engine vacuum. Performance engine builders recommend mechanical secondaries over vacuum due to tuning issues.
The advice I got and followed was to go efi. The car is less "rich" (raw fuel)at idle. Low speed 1300-1800 is significantly better. Better throttle response/control. MPG up to 15 from 10.
I went with fitech. They do have a dual quad application that may interest you.
Good luck