The starter doesn't care about polarity. If they converted it to negative ground, and they knew what they were doing, the negative side of the coil should go to the distributor. A positive ground would have the + side of the coil going to the distributor. However, there is a good chance that whoever converted it was clueless that coils have polarity. Permanent magnet motors care about polarity, and so does the radio and the ammeter.
