pre 88 had a quarter light, with the mirror half way down the door. Post 88 has a single piece of glass, and the mirror is at the front of the door.
Big bumpers were fitted after 1990 and the electric system was changed. If you plan to get a MK2 for a project and plan to fit a bigger engine, a post 90 is your best bet as MK3 engine looms plug straight in
Edit: Here is a 90 spec MK2: