As far as helping out...I am out of commission for a little while. My M42 had a timing chain oops, and I am having a custom motor built to replace it, so I don't have a car at the moment. I also fly to Seattle for work every Sunday-Monday, so that doesn't help anything! I bet I can work out a Saturday to check it out though.
At this point, it sounds like the issue is just going to end up being ONE stupid thing. If it is getting fuel and spark, and the crank sensor is working, it should run. If the fuel or spark was malfunctioning, it should at least run POORLY. The total lack of running indicates that something critical in the control system is pooped out or disconnected. Have you cleaned the idle control valve? Does opening the throttle when trying to start it help at all?
The motor should at least run (badly) if the throttle sensor or air meter were busted. The same goes for the ignition coils...all 4 would have to be totally dead to prevent it from running at all. I think that something in the controls is pooped out so that the ECU is not firing the ignition coils, because if you have fuel, some ignition activity would lead to some sort of operation.
Did you remove the ECU entirely? Did you shake it to see if anything was rattling around inside? I would assume that a loose EPROM would mean that you got NO fuel injection at all, so it seems unlikely that this is the culprit. Since the car died while driving, it obviously isn't like you unplugged or switched something.
The one other thing I can think of is that the ignition coil driver IC crapped out. It has happened. The coils get constant 12V, and the ground gets switched through the ECU, so getting 12V at the coils isn't indicative of anything other than that the main relay is working. Is there anyone local to you with a spare ECU, or just the one out of their M42 that you can plug in to see if that helps? At this point, a dead ignition driver IC seems like the most likely culprit. Sorry I didn't think of that sooner.
I'd lend mine to you, but the car is 20 miles away and not running lol. There are other Bay Area guys on here...surely someone can lend a hand and ECU!