I bought a Pertronix III and their recommended high-output low-resistance E-coil from Summit. The car runs terrible after it warms up. ... The distributor module is triggered off the distributor's points cam!
Interesting. I have never seen their new Ignitor III. Sounds like a step backwards. I think all their prior designs have a special ring that slips over the distributor cam. I recall an old electronic conversion that used a photo-detector shone off the cam surfaces to trigger, that was sold in the J.C. Whitney catalog. Never saw one in person. Maybe Ignitor III uses that type of pickup. I bought the more expensive Crane XR700 long ago that uses a special slotted plastic plate that slips over the cam. They claimed 0.1 deg repeatability (suspect). I had the IR emitter fail in one, and they require keeping the ballast resistor, so an older technology like the Mopar ECU.