Has your gasket blown, or are you just being cautious and want to fit a new one?

IF yours has blown, then skim the head, when you fit a new one.

Unless you know the block is flat, i wouldnt fit a metal one personally, they just arent as forgiving.

To flatten the block means taking the engine out and then stripping the engine down, as when its skimmed swarf will go into the oil and waterways.