Hi Rob just a little info. I believe that rear guard will fit the 91 & 92 models only. The 89 & 90 model YZ's have the same tank/shroud plastics as the 91/92 but the 91/92 had different side number plates and rear guard. They were somewhat "integrated" on the 91/92 models. In other words the number plate flowed into the rear guard if that makes sense. Google image the bikes and you will see what I mean
And of course the 93-95 era was a completely different set-up. New frame, all new plastics, low-boy pipe, etc, etc.
Hope this helps with the sale.