If the shift levers are very squared off, its around 1990-1, smooooth ones appeared later.
Having seen your bike, I would say 1990 going by the colour. Our local shop sold CB so we were all instant experts as we tried to out do each other on our purchases.
I thought I'd won with my 531 Magnum tubed Spectre but then a Shaman popped up with DX so I was left a red faced second. We cried foul though as his parents had bought it!
I'd put a USE post in my Zaskar in october 1993 - it was the first 'upgrade' it had received