They are handed.. or at least, they should be.
One is left hand thread, the other is right hand thread... that's how you adjust the tracking.
I'm not sure they are on the Disco. I know on the Series and my 90 they were but those had solid track rods where as the Disco has an adjuster on the drivers side of the trackrod because the main part can't move cos the steering damper is connected to it.
If the adjuster has the lefthand thread then both balljoints could be righthanded?? :-k
The steering arm (steering box to front of axle) does have a left & righthanded balljoint on the 300 series cos the drop arm on these doesn't have the built-in balljoint.
Or am I just talking rubbish? :-#