Got a call from the machine shop yesterday and had to go see this for myself.

Yes, this is a cracked Navistar block. Main web. Interesting that the crack is starting at the top and working its way down. There are big stress risers on the top of every main, apparently from something in the machining process. I'll get more pictures when I go back. I had 2 blocks and the plan was to build the second block for my dually. I guess the dually gets a Cummins now...