Briggs and Stratton Intek Plus 18.5HP How Flat does the head need to be for copper gasket?

[Auto Doc's]

I say don't overthink it. It's not the space shuttle. Sand the surface to true it properly, spray the gasket with copper coat and let dry, then reassemble. Copper in the oil might be minor initially from the copper coat spray on the edges of the gasket. There is really no other copper in the engine itself.