What was changed? You probably have already, but I'd check every wire, for continuity and shorts to others, on any branch of the harness that was changed.The GM harness does requires some modification.
A short seems unlikely, but if it connected the signal wires for 2+ coils together, you could be firing early. However, as you said, other cylinders should fire. I was trying to think about what could cause a firing to stop the engine from turning. Another culprit could be the position sensors - that's my best current guess.I have not tried checking for a short in the coil harness. Would this be a short to ground? That being said, would a short in one of the coils prevent the others from firing? (i.e. even if only half the cylinders were firing, shouldn't it sound like it's at least trying to start?)