cheers Alvyn, yeah, i don't have a problem checking the flatness etc, i'm more unsure about the surface finish really, due to the slight corrosion etc that you inevitably get on the face round the waterways.. two issues really - pressure sealing round the firerings and fluid sealing round the water/oilways..
It would be a right pi$$er if it leaks fluid after it goes back together, for the sake of not getting the face skimmed, but at the same time i don't want to take material thickness off unneccesarily if it's not needed...

it will come completely apart whilst it's off to check valves, guides etc and replace stem seals.