Really weird ignition issue...

It is a stock long block but has a 340 cam and a small Weiand intake.
Three different carburetors with the same issue?
I doubt that. I appreciate and understand the thinking on that but This Edelbrock didn't show this issue when it was on the 360 on this car:

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I have at least 5 more of these LA series electronic distributors. I may swap in another tomorrow and report back.