I keep thinking vac leak & most of the time the valley pans seal well & sometimes they dont. I'd take the clusters out & blast the brass tubes with the holes along the length of the tubes etc with brake kleen and also the recess where the clusters sit plus blast the idle mix screw ports on the chance that it is the carb idle circuit. Might block the metering rods up so you are on the power circuit (tho I ain't sure how much the power circuit is working at idle on eddies) and open up the idle mix screws all in an attempt to richen it & compensate for a vac leak if that is indeed the issue & take it out for a spin & see how it acts. We gotta get this before you trade back for the vette