Removing Oil Gallery Valves Mi16 head

Does anyone know how to remove the two cylinder head valves in the Mi16 head without damaging them? They're the ones which regulate supply & hold oil pressure to the hydraulic lifters.

I remember when I fitted them they were very tight & needed tapping in with a small drift even after applying a smear of oil to the O rings.

Thanks

After messing up one, I took my head to OW for the second. He carefully screwed in a small bolt, the thread just slightly mashing into the plastic, and withdrew it.

One new valve was about $27.

Thanks Adam. I 'll give that a try this week with a suitable metal thread bolt.

I was aware of the horrendous price so wanted to save them.

Jeff