The next phase is to machine one flat surface on each block, to do this I used my homemade Fly-Cutter, with a HSS tool bit sharpened just right!
Because my mill has a 4" vise, I had to remove the jaws to gain a little extra opening! Then I used a pair of "Starrett #54" hold downs to pull the block tightly to the floor of the vise, then I machined the opposite surface perfectly flat & parallel.