I don't think that surface is supposed to be absolutely flat. I know someone who ruined their HK 3.0 by lapping it and taking the curve out. Do not lap that block! It has a curve to get better clamping force when bolted down to give better temps. Who cares about the scratches on the bottom. That's what TIM is for. On the top however should not be scratched but you can take some polish to it or better yet have it nickel plated like a few I have seen. Looks damn awesome!
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