FINALLY; it runs with some authortity!!!!

Bill, Back to the too rich thing.
I'll try to keep it simple for troubleshooting ( for my benefit not yours ) :D

So the engine sees the following conditions:
( this is my understanding, please correct if need be )

Idle: This is tuned with idle adjustment, sounds like you have this part figured out.

Transition throttle : I'm not going into that just yet. I've broken this point out so I don't have to include accelerator pump shot into the part throttle pieces.

Part throttle ( no boost ) : Tuned with main jets and maybe power valve depending on what vacuum it has at the time.

Part throttle ( boost ) : Tuned with main jets, power valve, vent tube extensions.

Wide open ( boost ) : From your wideband this look fine ( until you start messing with other stuff ) :lol:

I had the same issue that you're going through. Way too much fuel at part throttle and fine at full throttle. Sounds like too much main jet.
Mine was 13.1 at idle ( for some reason it wouldn't idle right any leaner than that )
10.2 at part throttle and 11.4 at full throttle.
I downed the main jets from 74 to 68 on the 350 holley, lengthened the vent tube about 2 inches into the inlet piping, opened up the power valve holes ( to what I completely forget ) and the issues went away. Now I did have to play with the whole accelerator pump shot a lot afterwards to get transition throttle to behave correctly.

What mains are you running and where do you have the regulator reference port connected?

Oh, and I'm not sure what would make me smile more, the sedan going sideways down the highway, or seeing 2 old geezers in that car going sideways down the highway.

This thread made my week! Keep up the good work! I love that car. You guys rock!!!