Mick, have you tried adjusting the mixture screws in the baseplates of the end carbs? Backing them out maybe 1/8 turn each will make a big difference and take some of the load off your center carb. I have set up more than a few 6 paks and even with big cams, I've never had to open idle passages in the center carb. Good luck!
VERY good advice.
Also, I am not aware of any metering block idle mixture passages under the metering block behind plugs???
There are main circuit passages behind the power valve at 3 o'clock & 9 o'clock that can be enlarged per the old Direct Connection book, but I don't recommend doing it. There are also some holes up in the top corners (name?) that can be enlarged too, but again I don't recommend it.
I know you have that big stroker hemi six pack, so maybe consider Promax parts instead of modifying stock pieces. You can get adjustable metering bodies & adjustable metering plates.... but try the outboard idles screws first like Lee says. THOSE are behind lead plugs on the front of the baseplates for the outer carburetors. Hope this helps.
