[BB427]

Check the idle circuit air bleeds on the top of the body next to the acc. pump squirters. Something may be blocking them or they may need to be opened up larger. Mabye .002 or so. (not much)
This can be done with a small wire bit by hand.

What position are the throttle plates in and are the boosters dripping fuel when at idle?
As far as jets go , if you look in the Holley book a great number of jets actually have the same size hole. ???? I have never understood this. you may make a change and not really make a change at all. Buy good aftermarket jets that areflowed and checked then you can make proper adjustments.