Is there a reason you can't throw a crank and piston/rod assembly in a bore and check it that way? Pretty much every aftermarket set of pistons has a CD within a .001" and a set of rods made by a good company have about the same C to C distance. Throw the same piston/rod in each corner and you know if the decks are parallel while you are at it.
No special tools, and more accurate than a tape measure and straight edge.
Stock rods lengths can vary a bunch, I've seen 426 M.W. rods have .008 differences in the center to center lengths
another thing to keep in mind on stock cranks is having the rod journals exactly 90 degrees away from each other at the top and bottom of the stroke, lots of them don't
Lots of errors on most mass produced parts in our cars