Solution:
Thanks to @mysocal911, there are really three critical circuits to look at. Open the ECU, and take the back metal plate off. Check the three solders in these pictures. Upon close examination, I could barely make out little hairline cracks. I reflowed some solder over them, reinstalled the ECU, and problem solved.
To save everyone some time in troubleshooting, my takeaway is this - DME relay first, if not resolved 80% of the time it's the DME ECU, check those three solder joints. If you're unsuccessful, well then you still have another 10% ref/rpm sensors, 10% misc (wiring, ignition switch, head temp sensor, etc) chance that you can track down.
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