Does it have an aftermarket alarm system in it with a ignition power cutoff relay? That power comes directly from the ignition switch. Look to see if there is a relay spliced into the switch wires under the drivers dash panel. It's possible you have passkey issue if there's a pill resistor in the key.

The fat red wire on the HEI cap should have 12 volts on it when the ignition is on, chase the power failure back to the ignition switch.

The only part left is the *pick-up coil" under the rotor. The distributor must be removed from the motor and the drive pin driven out with a drift from the distributor gear so you can pull the shaft out to replace the HEI pick-up coil

Inertia switch.

Timing chain.

I always try replacing the entire distributor with one that I know works. This typically will rule out all distributor related problems.

Typically, there is a primary ignition system, and a secondary. Swapping out the distributor pretty much rules out the primary ignition system.

If swapping the distributor doesn't help, I would continue to swap your spark plugs, wires, and swap out/inspect the ignition(and any related) fuses.

Make sure your ignition coil is not wired backwards. Really inspect your spark plugs, and swap them out anyways.

Cheers.