I am assuming this is being done manually with a die grinder and long reach burrs, stones and drums? Or are you CNC porting this head? I always just do a quick and easy gasket match port and polish job. Worry more about smoothness than port size to maximize flow.
The castings are cool, are you just using them as a guide for your port job?
This guide is old, and I like using burrs better than grinding stones and sanding drums, but I think it is a pretty good general outline.