Runs 20 then dies

Problems like this can be tough. The coil was a good bet. I'd bet on the ECU before the dist, but try to do some testing to see. Carry a big long clip lead with you. If it quits, run a jumper from coil+ to the starter relay battery stud and see if it starts / you have spark.

Unbolt the ECU, clean it and the firewall, and reinstall with star lock washers. Remove and "in - out" the connector a few times to scrub the terminals clean. "Feel" for how tight it fits. While you are at it, not a bad plan to do this with the regulator connector, as well.

Same with ballast resistor and ESPECIALLY the distributor connector, which has very little current through it. You might get lucky