Ken, you are right. The early flywheel has less teeth than the later flywheel.
If you could count the teeth, that would tell you which flywheel you have. The other way is to determine if your starter is a 6 volt or a 12 volt. The 6 volt starter would indicate the older flywheel and the 12 volt starter would indicate the newer flywheel. However, you could have a 6 volt starter operating on 12 volts.
If you can count the teeth, the early flywheel has 139 teeth and the later flywheel has 168 teeth.
