I have measured it with a micrometer. I also set the block on the bar on the mill that indicate in and measure off that. All that will tell you is if the block was maybe never machined. The blocks I've measured over the years (many of them never touched) have been all over the board. If you want to do it like people THINK blue printing is, you start with the crank and get it indexed so all the throws are equal. Most aren't. Then, you need a Tobin-Arp machine to equalize the rod lengths. Most are all the same these days but stock rods are usually crapola. The issue I've found is some rods, even rods finished here aren't always exactly 6.123. Which isn't always bad, if they are a bit long and they are the same. Then you do the math, find the deck height you need and machine the deck.
Or, you check all your lengths etc, rough bore the block, slide a piston and rod in all 4 corners and write down where they are relative to the deck. Find the low corner and machine to that, plus what you need to get the deck clearance you want.