Deck height

Its not just a simple crank CL to deck- you also have to correct the crank/cam CL to deck angles- 45 from Crank/Cam CL and 90 to each other, along with parallel to the mains. It requires a special fixture or a CNC with indexer, not just a surfacing machine. You need a point of reference other than the OEM decks that are far from accurate. You need to line hone the mains first to really do it right.
Going off the 4 corners only tells part of the story and is still a matter of tolerance stack.