You may not be able to get same length shanks, and even if you do you will still need to reference them to the same length. If you make a collar to fit the shank and lock it off at your Z 0, you can then do the same to ensure your other tool has the identical protrusion. I use a length setting press and all of my tools always are exactly the same length. I have to admit it is easier for me as I only use 3.175mm shanks. G.