Stumped and Frustrated with a Holley 670 Hesitation

From what I've read so far, this is not a secondary problem. You're either going lean in the primary or your timing/ignition is acting up at the hit/load. That #31 nozzle should be plenty, so I have to wonder if you're running a vac advance hooked to the manifold vacuum? Even being a little lean on primary jetting shouldn't cause it to dump at low speed full throttle? Is the primary float level consistent?

Anything else you can think of may help. Either the carb is bad, or we're just missing something? I'll keep thinking on it...