I would think that the way to match up two sliced heads would be to cut them roughly with whatever you have that can do the job within .200" then mill them square and flat to mate.
I'm a bit in awe of someone doing this; that's a lot of internal cast iron topology to seal, oil+water+vacuum.
I sliced up a head in my favorite motor to see where I could make certain mods, the internals of the casting were messier than I assumed (and oh believe me I assumed they were rough).
This engine's at the opposite end of the spectrum, getting OT here, tangentially related only to the modded head. I, too, will shut up now.
http://www.wps.com/AMC/195.6OHV/Cracked-head/index.html
