Chris, as you mentioned, replacing the resistance wire on an early Mustang (and other early model cars) is easy, as the ignition switch is mounted in the dash.
My question concerns doing the same electronic conversion in later model cars with the ignition switch in the steering column.
Rather than trying to replace the resistor wire in the steering column (pain in the neck), could you run the resistor wire to a relay and then get your 12 volt feed for the coil from the battery or another constant 12 volt source??
This sounded fine in my head (amongst all the other voices), for two reasons. 1, you don't have to climb inside your steering column to replace wire and 2, if you got your 12 volt feed directly from the battery (via the relay), there'd be virtually no chance of voltage drop.