To be honest, I wouldn't bother trying to remove enough material to get rid of the dents in the head.

Just get rid of the high-points (you can even use some small files for that) and put it back together.

We're not talking about an expensive, hi-performance racing engine here, it's just an OS sport engine.

If it really worries you, just buy a new head but I think you'll be surprised at how little difference it's going to make.

At the reynolds numbers we're talking here for the gasflows in the squish-band and combustion bowl, dings small depressions such as those shown in the photos will make virtually no difference and at worst it'll probably cost you 100-200 RPMs compared to a new head.