Does the Eldebrock have the float adjustment like the Holly. Ive only had one about 25 years ago so I don't remember. If so that would be something to check.
Also if the car still has the fuel pressure cut off, you could have a bad connection. Try bypassing that for diagnosis.
When it chugs while giving gas does it appear to be over fueling (flooding) or lack of fuel (lean condition)?
I'm assuming lack of fuel from what you describe. Also check voltage at battery while running to see what your alternator is putting out. You mentioned problem started when turning on the AC.
You could have something wacky going on with voltage/current supply to the system.
Your voltage should be approximately 13.5 to 14.5 volts at idle.
Just found a good link on adjusting eldebrock floats. Obviously they are not externally adjustable but looks easy enough without removing the carb.
https://www.youtube.com/watch?v=gXQ_mJhlZ0MAlso a fuel pressure guage may be necessary to assure you're not going over 6 psi