Misfire at cruise, popping/afterfire at 3000RPM

Righty Tighty said

Yeah, it’s pretty frustrating. I’m on my second distributor, second coil, two separate ECUs, three different engine harnesses, valve job on the heads. I’ve checked and double checked timing.

One thing AJ suggested was reversed polarity at the distributor pickup, but I don’t understand how that could happen with all those different harnesses and both distributors. I’m not doubting him, I just don’t understand.

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Wow that's a lot of changes. just spitballing here but you know for a fact that you're out bored carbs are full according to site bowls? 2And are working properly I think you could still be looking rich on your plugs if you're out bored carburetors aren't opening and letting air in under load. Have you unhooked your linkage and pulled vacuum on your outboard carb pots to see if they're opening freely and properly?