Cylinder head skimming help

Guys, how far can you safely skim a cylinder head? Reason I'm asking is the head I took off has damaged cam bearing surface and I expect that will be very expensive to have fixed, but I have another head which is better but has det damage but will need about a millimetre skimming off to get it flat. Problem is it's already a millimetre below nominal. Is it worth doing or do I phone Bob on Tuesday for a new head?
Cheers
Paul

Wouldn't you just use a thicker head gasket to keep the comp ratio and clearances the same ?

I suppose but there has To be a limit, I know some heads have a Max before the walls of the head get to thin around water ways etc.

Find a better head to work with. both you heads sound likely past worthwhile refurbishment .

How do you know how much has been already taken off out of curiosity?

Cheers Mr B, I shall get on the case after payday.
Woody, nominal cylinder head height is 136.9-137.1 iaw manual. I just measured the one with det damage with a vernier and it came out at 136.15 so nearly a mil lower so probably been skimmed a good few times in the past!

ah cool, thanks mate, that's good to know.

some of the head and block measures can be found in below pdf .
https://drive.google.com/file/d/0B7Ub2apq5-pfTHlJWmpEQzNnT2c/view