Hei /6 won't shut off?

A simple way to bench test ignition is to attach a plug to the coil directly skipping cap and rotor. Use a battery to supply power, rotate distributor shaft and observe spark intensity. A string is a simple way to do that. The plug gap can be opened to about 0.04". It is important to keep the ground strap parallel to end of tip terminal. This results in a uniform spark and long wear life. Never contact tip nor ceramic when adjusting, or plug may be damaged. The ground strap typically chopped off square, but if the ends are radiused it gets rid of sharp hot spots that can preignite. Some high end plugs come that way.

If you have a scope with a high voltage probe 1kV or more, the primary voltage can be observed at the - coil terminal, and multiplied by the coil turns ratio. It is possible to measure spark duration after the initial strike, by viewing the decay after the large initiation strike. More duration indicates more energy. Larger gap shortens duration. The wave is best stored for that. A low value 0.1 Ohm or less shunt resistor can be used to observe the primary supply current ramp during coil charge. Current probe can be used too, but they are very expensive. From the current ramp, the peak current can be measured. Current is calculated by dividing the voltage by the shunt resistor value. Coil energy increases with the current squared. The coil inductance can also be estimated from the ramp time. The HEI has a controlled current. Well that is a start. There may be old posts by me with more information on this forum.
I am no expert, but just work with this as a hobby I enjoy.