So you simply proved it is lean and needs more gas at idle. Now you say it is rich... well I hope so as you took half the air away from the emulsion tubes, and are drawing harder on the idle fuel feed restrictions in the end carbs, with the end carb idle screws at 1 full turn. It will be rich at 1 full turn. Until you measure the metering plate restrictions who knows what is in there. I suggest a holley carb manual by alex walordy so you understand how the idle works. I would say you need bigger idle fuel feed restrictions, made bigger .001 at a time. I am assuming the idle air restrictions are stock size. A metering block for the center carb that you can adjust would be good. I used a 600 or 650 double pumper plate on mine to get the drillable idle feeds. You adjust the fuel feeds .001 at a time until it idles with the center carb at 1 to 1-1/2 turns, ends at 1/2 max. Timing needs to be at least 25 on the crank and stable, not bouncing around. No magic here, the idle will take work, I am betting the center carb is open on the transition slots at idle, as a 512 needs more air than a 440, and I don't even want to get into fixing that.... but here goes. It would involve drilling throttle plates, not allowed on this board, most on here think any 6bbl with drilled plates has been modified, no it is factory. Bigger motor, bigger holes, .002-.005 at a time until it idles with the plates closed. Oh one more thing, that big hydraulic cam will not idle clean at 800 rpm like the big roller cams most guys use, so you guessed it, you need more air for that too, bigger holes. Now you know if you really want to fix it.