Got a couple more minutes to tear into the truck today. Looks like it was definitely a case of someone leaving the rod bolt nuts loose. It did break the lower part of the cylinder in addition to bending the exhaust valve, breaking both the rod and piston, and probably trashing the crank as well. In hindsight, I wish I would have shut it down sooner but when your in traffic you have to make choices. Oh well, live and learn.

On the plus side, it should be back together pretty quick and better than it was when I'm done...