It is better to machine the head rather than the liner. Just remove material from the head and you can use shims to get back to what it was before. Should you mess it up completly you can always get a new replacement head too. Compression ratio seemed okay on mine though, while the poorly made intake was a power robber.

It will never reach the power of a Norvel .15 though, never mind power to weight ratio.

I saw that you tried the larger intake on the Norvel (I'm surfer_kris on rcgroups), great engine isn't it?