Originally Posted by slartidbartfast
That's burned paint, not stained metal. I'd leave it alone. Consider it a badge of honor, a warning to others, ... whatever.
Replace the oil window, oil and filter, keep your eye out for leaks from any cooked seals and if nothing bad happens, consider yourself very lucky.
I'd replace the valve cover gaskets (all four of them), they saw a lot of heat and probably aren't as flexible as they used to be.