> Not having thought about it too hard, if the three norths all align at -2 degrees west longitude, wouldn't they also be aligned at 178 degrees East longitude, somewhere near the east coast of New Zealand?

There is no required equivalent 'three souths' alignment because the Earth's magnetic field is not a pure dipole. Higher-moment variations can cause essentially arbitrary (but small) deviations of magnetic north/south from its dipole approximation.