If the head is all pitted and damaged you need to determine the cause.-------Either the motor was apart before or it needs to come apart now.----You say there is no compression ??
parts are pretty easy to find with .20 o.s but I belive they have some .30 o.s parts to. only go to .20 if you can, it would be cheaper and if a problem did occur again you can (simply) change to .30. Pictures always help!
It is very rare for a Piston Ring to break and not damage the cylinder. As for milling the cylinder head, if the ring put a bunch of pits and marks on it, milling is not going to clean it up.
You can mill .030 off head and any remaining indentations will fill in with carbon,,,wont hurt a thing. Just make sure there is no metal remnants of the ring embedded.
