Would not be the glow plug relay when hot.
If you're spinning over, like coozie suggests, unplug your ICP, then try it.
Also, while you are cranking, have you tried giving it pedal? If it was ICP related, and it was reading it too low, and the IPR was kicking it too high, it would not start, until you goose, in whicih it would thing spring to life very harshly.
Another possiblity is your under valve cover wiring harnesses.
I forget what happens if you unplug your IPR, and try to run it, but you may also try that.