I rebuilt the bottom end on my NC30 over the weekend. Everything when together really nicely and is moving freely, but I do have one question about the piston ring rotation...

How critical is it to maintain the degree offsets between the ring gaps as per the service book?

When I installed them, I made sure that the 2 compression ring gaps were offset from each other and the 2 oil control ring gaps were offset from each other and the 2 comp. rings, but I didn't notice the specific degree angles until after I had bolted up the cases.

I don't think it is an issue as the rings can rotate anyway, when the piston is moving but was wondering if anyone can confirm, otherwise I'll just worry and probably take it apart again!

I wouldn't worry about it. You said you did offset them.

As long as they are offset no problem.