Firing un-order?

Pulled the plugs and noticed that 1,8,4,3 where tan-ish. Plugs 6,5,7,2 were clean as a whistle. Same goes for the exhaust ports and tops of pistons. Thought the carb primary on one side of the dual plane intake was set bad and caused this, but that's not how the ports are separated. Then I realized that this difference is on the 180 degree rotation of the firing order, not the other. Any ideas on what is causing this?

My thought was distributor or distributor cap. The odds of the plugs or...

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Author: Juan Veldez