It'll still fire with it being 180 out. What typically happens is it will backfire through the carb.

To start diagnosing, I'd pull the coil wire of the dizzy and set it close to ground. Next, disconnect the mag pickup line and tap the exposed pin on the plug to ground a couple of times. If the ECU is functioning correctly it'll trigger each time that pin goes to ground.

If it works, it's probably the mag pickup. If it doesn't, I would check the wiring, check the ground to the ECU, check the ballast resistor, check the inner and outer windings on the coil with an ohm meter, and then finally replace the box with a known good one in that order.