HEI conversion problem: no spark while cranking

RedFish said

All aftermarket and wiring changes aside... When you get a single spark as ign' switch returns from start to run, the fault can be the ign' switch. I would disconnect and check it at its harness connector under the dash. If good there, my next stop is bulkhead connector.
What I'm saying is regardless what we do downstream, we're still relying on a lot of the cars OEM wiring and components.

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If you are referring to my symptoms listed above, the "lone spark" was during Start, while cranking. The key was being held at Start and the one spark occurred during cranking.
I certainly agree that we are dealing with wiring components that are far older than Chrysler ever considered them to be operating.
Incidentally, when I checked for spark just by cycling the key, Run to Off (engine not running). I did not get any spark.
During the troubleshooting process, I straight wired the relay to the battery, bypassing the ignition switch, harness, etc.