I am not familiar with the 4180, but just reading about them in various Articles quickly makes me conclude they are not compatible with a Performance Engine and they are not Universal Carburetors but made specific to Emission friendly Engines? IOW changing your Headers is requiring an adjustable (idle mixture) Carburetor to tune for the new Parameters which means 4180=NO GO! Sorry........
And again playing with your Plugs Heat Range won't make any difference on your Header/combustion Temperature.
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