Did you test the pickup coil in the original distributor?

How did you connect the Unilite? It does not require the Mopar ignition amplifier box (the thing you call the ECU?), it just gets power, ground, and has an output to the coil. If you connected it as you would a Mopar distributor, yeah, it could burn up.

The alternator might not have liked getting reverse polarity, either.