Something that seems to have been ignored::
MOST factory ignitons work somewhat like old breaker points, except the electronics turns the coil on and off rather than the points.
GM HEI is a bit different but it is still, in the end, "a switch."
Kettering, loosely, covers breaker points and the above
CD means "capacitive discharge" and it works sorto' like a photo flash. A high voltage power supply (inverter) charges up a relatively large condenser/ capacitor, and the spark trigger discharges that cap across the ignition coil.
CD does NOT have DC current through the coil like the previous units. MSD stands for "multiple spark discharge" (at some operating RPM)
There is some opinion, that in certain conditions, the very "sharp" spike of a conventional CDI may not fire fouled plugs, where, the broader, more powerful HEI spike might. In other words voltage along might not be the only thing.
Many of us here use a GM HEI module. When my car was together, the HEI even fired a factory Mopar coil.
Pertronix is not CD. It is similar to Kettering. Many like them. Only downside I see to them is parts. If it dies, you better keep spares in the glove box, as most parts stores don't carry them.