.18 is the min you would really want in a cast iron block. But the thicker it is, the better. The "thrust" side is the thickness you should be concerned with. It can be thinner on the non-thrust side, but I would never go below .15 on the non thrust side.
I sonic all of mine, regardless how much I bore them. Too cheap of a process not to. One block with core shift could ruin a whole build.
Brian
