You need to try and figure out if this is a voltage supply problem or an ignition problem
1 Pull all connectors, the ECU, the ballast, and the dist, and work them in/ out to clean them. Feel for "tightness" of fit, and inspect for corrosion
2 Turn the key to "run" with engine off. Hook one probe of your meter to the blue field connector on your alternator, and the other end to battery POSITIVE. You are measuring the harness voltage drop and the lower the better. Anything over .2--.3V (three tenths of one volt) is getting too much.
3 Clip your meter to coil + and battery + Crank the engine USING THE KEY and while the engine is cranking, read the meter. Once again, you are hoping for a very low reading, below 1/2 volt.
4 Check the gap in the distributor reluctor/ pickup. O'Really has brass feeler gauges, you need a .008". That's inches, not mm. While doing this, check the reluctor and pickup for rust, debri, or damage.
5 You can also hook your meter on low AC volts to the two pins on the disconnected distributor connector. Crank the engine, and the dist. should generate about 1V AC
6 Check the resistance of the coil when disconnected. You'll have to tell us what coil you are running as many are different.
7 If you have good voltage at the checks earlier, next, hook your meter to the battery and crank the engine. You should have ABOVE 10.5V the higher the better
8 Double check at the coil + Hook your meter to the coil + and to ground. Crank the engine using the KEY. YOU should have at LEAST 10.5V or better
If all the above seems OK, make SURE you don't have a bad coil wire, IE how you checked the spark. "Rig" a spark gap to the coil using a known good wire, or use a grounded probe held near the top of the coil.
One last "trick" you can try to improve the spark is to hook a temporary clip lead from the coil + to the starter relay stud. DO not leave this connected long without starting the engine, and do not leave it connected long after starting the engine.
If none of the above results in any help, replace the coil (cheapest)