[Zero10]

I would stand behind your initial diagnosis of speed and/or reference sensor(s). Changing the one sensor makes perfect sense. They seem to be the first place to start looking.

Here's one thing I did for s***s and giggles.
Unplug the speed sensor (the back one), and put an ac voltmeter on the 2 output pins (the ones that you can actually measure a resistance on), then watch the AC voltage as you crank it. Sounds like they might be gapped wrong. It's a relatively simple check. For comparison, my freshly-gapped snesors gave me about 5 VAC when I was cranking the engine. Any less than 2.5VAC or so and the DME will not see the signal, since the pulses will still be a logic low.

I previously printed off a big troubleshooting guide, since once I finished my engine rebuild, I had no fuel injector pulse, and no spark, but I have since lost it, but I grabbed it from Clark's garage, under ignition troubleshooting.