[Tripower455]

I've got nearly the same setup, only with a smaller HR cam (for now..... I've got an Old Faithful STILL sitting on the shelf waiting to be installed one of these days).

As the others have said, the idle tubes need to be opened up. Mine are at .038 and can probably go another thousandth or so. I have a Jet "500 CFM, Circle Track" 2gc in the center FWIW. I've also got holes in the throttle plates. I can control the mixture with the screws, and it idles at 750-800 with almost 20" vacuum (with vac advance).

Once you get your center carb figured out, I'll bet that you're REALLY rich on the end carbs with 74s in them.

I also changed from 6X to the 290 KREs. With the 6Xs, 73s were a little rich at WOT (11.9-12.3ish AFR on the LM-1). When I went to the KREs, I also installed a CVM ported aluminum intake and ported end carbs. My AFR went down below 10 at WOT, blowing huge clouds of black smoke all the way down the track. I am down to 65s now (my carbs are set up for Holley Jets). I am assuming the the far more efficient chamber of the KREs is the reason, but I was stunned at how small I had to go.

The car also lost that hesitation when the ends opened up that it had running so rich!