Are locknuts on threaded headsets reverse threaded?
 

Is it tight or am I turning it wrong?

It's an old campy headset.

I've never seen one that was reverse threaded.

Not that I know of either.
It's possible that the locknut has corroded a bit onto the steerer tube, but liquid wrench or something should take care of that. If you have two headset wrenches it will probably be easier to get the locknut unstuck.

Just be careful. I recently had one lock up, and it wouldn't turn with the wheel tied to the down tube and a 3 ft breaker. I finally had to cut a flat spot on it, and go right down to the threads to get it to release. PB and a 3 day soak didn't help either.,,,,BD

It came off. Frame and fork are now ready for sanding.