Firstly, get it checked for cracks. If it's crack free then you can rebuild it. Then have new valve guides pressed in (if necessary), skimmed etc, no problem. Here in the UK I had my M20 head skimmed for £15, the rest of the re-assembly was done by me. It took a few days but the car runs lovely now without having sooty piston-tops or a smoky exhaust.
HTH,
Shaun M