GM Coil and Module Help Required

I think you are incorrect about a couple things here. The alternator field does not cause a spike as long as the alternator is (normally) connected to the battery. The VR pulses the field to regulate. The coil field affects the module? No. There are hundreds of thousands of GM in cap HEIs in service through the years, some of them still RUN. I just ran into one the other day, an older pickup, and it had the original coil and module. Only thing ever changed was the cap and rotor.

Actually, effects, damage from EMI can more easily occur with an external coil / EFI, because the trigger wiring is longer, and if improperly routed, can be subject to interference from the secondary wiring, especially if solid core is used.

This was famous with MSD, known for "retriggering itself" due to the spark current causing a trigger--in the trigger wiring