I have an '86 and I just installed a UFO 85-87 KX fender on it a couple days ago. I cut the side mounts on the frame about half way off to get it on, and trimmed about .200" from the fender at the front sides to fit between the frame rails. This weekend I plan to remove the rest of the frame rails and weld on the ends that I cut off for a factory look.
I also have an '88 that has a UFO universal fender on it. The bike came like that. Whoever did it just wedged it in and left the side mounts out in the open.
If I get my digital camera back tomorrow, I'll post a pic of both.