Paddocks list 2 different part numbers for series 1 discoveries, though from what I've see the mountings are the same and some of the aftermarket manufactures just make one part number for the rear of all series one discoveries.
If its a case of 'can I put 200TDi dampers on a 300TDi' or vise versa, then I should think so. However something like the damping characteristics may be different so I would make sure both dampers are either one or the other, not mixed.