I've gone over a head & block with a piece of wet/dry on a very flat piece of hard Maple(a very stable hardwood), very lightly to clean it before checking it with a Starrett straightedge & feeler gauges to check flatness. But I wasn't fooling myself into thinking I was 'Surfacing' it. Some I did have surfaced. Flatheads use such a thick gasket that Copper Coat will seal them if not too far out.