There is only a few thou available for skimming, so no room for error and only to be done if deemed necessary. However it must be measured to ensure it has not been done already. Go to someone that can be trusted and comes recommended.
I only suggested skimming once you knwo ehre it has blown through. I have had 5 k series engines on my metro and a few of them i did skim and they never blew again however i had them check on an engineers bench and used my laser level!. However I always found that it was between piston 2 and 3 water chamber nearest the piston. You can just replace it and I would recoment the Landrover Gasket kit as its uprated slightly.