Hi everyone, thanks for your replies.
Basically, because of the pitting on the block face the machinist thinks that approx 20-30 thou needs to be machined to get the face back to a smooth face.
Currently, my pistons are about 10 thou above the block at TDC and I have a 40 thou gasket, therefore I envisage that the new gasket I'll need to return me back to the origanal CR will need to be 60-70 thou thick..............hense the multi-layer cometic gasket which Burton's have suggested (not suprising at £100 a go!)
Oh, and to make things more complicated, the block is bored out to 94.5mm, therefore standard-bore head gaskets (92mm) are no good.
As I said before, because I'm spending a lot on this gasket and they've specify a surface finish of 50 microinches, I want to make sur ethat the job is done correct.