I certainly would check for rotor movement. Any reason to think the chain / sprockets are worn? Did it run wierd or make noise when it quit? When cranking does it sound normal, as normal compression?
1.....Is the ballast on the dead car 4 or 2 terminal, and is the ballast on the running doner 4 or 2 terminal? This is because older ECU's known as "5 pin" MUST have a 4 terminal ballast. You cannot tell by looking at the box. Many aftermarket, newer, "4 pin" boxes still had 5 physical pins. It's just that one was dead.
So a 5 pin box MUST have a 4 pin ballast, but a newer "4 pin" box can use either 4 or 2 terminal
2...Might be the coil wire, check for spark right at the coil by using something like a grounded screwdriver or clip lead
3...Disconnect everything from coil except two ignition wires. If there's a tach, disconnect. If there's a radio condenser on the positive wire, disconnect.
4....Double, triple check ECU for GROUND. It MUST be grounded. Once again, with key "in run" the coil will be drawing current sitting at rest. This means you should see the following voltages
On "key" side of ballast, "same as battery" or very near, IE 12.6 or so
On "coil" (this is same as coil +) side of ballast a quite low voltage. This will vary, and might be all the way from 4--8 volts
(Obviously if you hot wired battery to coil + it will be at battery voltage
On coil NEG terminal you should see a very LOW voltage, probably below 1 volt. This is because the coil is (or should be) going to ground back through the ECU. This should hold true whether the ballast is in the circuit or not
5...Try the trick of leaving the key on, and grounding first one, then the other, of the distributor harness connector terminals. One of those terminals should produce a spark, each time grounded. If so, the ECU and wiring is probably good
6....Wiggle your wire connections, especially the ECU connector, and inspect internally
7....Since you are "out" you might want to do a half assed hot wire/ rewire to see if the harness is bad YOU CAN ACTUALLY DO THIS with clip leads. If there are any parts stores, especially NAPA you might find one that stocks an ECU connector pigtail
With a 4 pin ECU this is easy:
You need about 5 clip leads from radio shack, let's eliminate them one at a time
A...Bottom left, carefully clip a lead from ECU to coil NEG
B...One pin CW, clip a lead to that pin, this will go direct to battery
C...Clip onto top ECU terminal, this goes to the insulated distributor (recessed) terminal
D...Clip one lead to right hand ECU terminal, this goes to the exposed distributor (male) terminal
E....Run a wire to coil positive, and hook that and "B" to your battery for testing