As an update, I checked conductivity in the harness from each pin (8,9,21 I believe) that leads from the ECM to each of their respective connectors at the coils and they were all perfect. This leads me to believe it is the ECM that is responsible for my problems.

Ordered another ECM that was said to be 100% working from eBay, received it and plugged it in. Started the car up and the problem persisted. Checked the originally affected coil (closest to the fire wall, fires cyl 1&6) and now it's sparking! But the next coil down the line (fires 2&5) isn't firing. WTF.

Swapping back to the old ECU reproduces the original result, new ECU shifts the problem to a new coil.

Is it possible that I received another dysfunctional ECU with the exact same problem as mine but on a different pin? I don't see any other possibility.