I'm Positive?

When this car was made it would have come from the factory with a positive ground setup, however over the years a lot of these cars have been converted to negative ground like the later cars.  In '65 the factory converted to negative ground when they dumped the generator in favor of an alternator.

Confusing, the negative lead should be going to the distributor  not the positive lead if it's been converted to negative ground.

Battery leads suggest that it has been converted, lead with disconnect is smaller consistent with it being the neg lead. 

After market fan on front of radiator

Leads for generator

Showing the positive lead coming to the dizzy

Given the size of the respective positive and negative battery terminals and the negative ground radio I think the car was converted to negative ground.

Aftermarket 8 Track radio with negative ground