I had a similar thing happen with a Nova, but my trouble came from using a higher nitro percentage. The advice I got was: change the button head and use a small amount of metal polish on the top (only the top) of the piston to polish out most of the pitting.

You also want to replace the conrod and may consider adding a .05mm or .1mm of head shims. I did this for my engine and it ran well, as fast or faster than before. Engine still runs and raced 5-7 liters after the pitting(detonation).

Not sure how big the scratch on the side is but if not too big should not be an issue.