can you just control the main dizzy through the ecu using 4 coils to the main 1st spark, and then just leaving the 2nd dizzy/CAS standard ? as the 2nd spark just runs off the cams and i assume it doesn't need the power unlike the main spark.
The ECU doesn't control the distributor. In Brad's case, the Alfetta distributor provides a pulsed signal (2 signals per crank revolution) to let the ECU 'sort of know' where the engine is.
That pulse will typically be at about 0-20* BTDC of each cylinder.
The ECU does everything else. But the position of the Alfetta distributor (in Brad's case) will also determine the base ignition timing and this must be set to match what the ECU is sending out during idling. Any advancing or retarding of the Alfetta distributor will effect all timing values at all rev and load points.