Dual ICMs and single coil will not work.
They should as long as RPM isn't too high. Minimum angle between cylinders is 90 degrees just like a V8. Six cylinder dwell is 30-35 degrees so if spark advance is limited to 30-35 degrees max I would not expect a problem.

two coils and a dual coil isolator
Years ago I tried to build a non-computerized HEI for high RPM use. I used a high voltage diode in each coil wire. Each coil was controlled by an independent HEI module connected to a four cylinder pickup coil. It seemed to work ok.