First, IF you are not changing it from 6V to 12V then leave the polarity alone, ^v works better with positive ground. Changing polarity should ONLY be done if you are upgrading to 12V.
If it still has the OE generator and you are changing to 12V the generator and regulator will have to be upgraded and then polarized. If changing to 12V the best thing to do is replace the generator and regulator with an alternator. Most conversions use a GM 12SI alternator with built in regulator, there are many wiring schematics on line for changing over or purchase a one wire alternator. You can make your own conversion with a used alternator from a salvage yard or kits are available to do it either way, a Google search will bring MANY how to's. Your choice.
As for the coil if changing to 12V I recommend replacing the 6V coil with a NAPA IC14SB which has a built in resistor or you can use your 6V coil but you must install a voltage dropping resistor.
As I stated in your other question the coil should be wired according to the polarity you want to use. If it is positive ground then the "+" post of the coil is connected to the distributor (ground), if it negative ground the "-" terminal of the coil goes to the distributor.
