Hi Phantoma,
As Deejay has suggested the code on the cowling will give the best indication of manufacture - provided the engine is original. I've noticed that the newer models have the later Rover decals (newer logo), a plastic cover over the clutch assembly, yellow pin stripe on the catcher decal and no metal ID plate on the rail (sticker instead). It's highly unlikely that anyone would want to make their mower look older so those things should check out also. There is always a possibility that a 20 year old rover has had a 5 year old engine fitted to it...
