If it were mine I would not want EE with 6 volts. With 6 volt, it is not uncommon that if the battery has to crank the engine very long, the battery charge voltage will drop below the minimum operating level of the EE module and you lose spark.
Just because it came from the factory as positive ground does not mean it must stay that way.
If it were mine and I wanted EE, I would install a 3 wire alternator that you don't have to rev to start charging, convert to negative ground (If it has distributor, reverse connections on small coil posts so -- post goes to side of distributor, reverse ammeter connections, and install a 12 volt battery negative to ground).
I would replace coil with a direct 12 volt such as NAPA IC14SB and not use a dropping resistor. You don't need a 40000 volt coil when the plugs need much less than that to fire.
Pertronix also recommends that you replace the solid wire plug wires with newer automotive type wires
In this day and age 12 volt negative ground will likely be less confusing to the person who may have to troubleshoot a problem.