I'm not familiar with the '87, but I know on my '82 CJ, and just about any other car I've taken a wiper arm off of, you had to grab the wiper arm and push towards the end to take pressure off a spring loaded 'latch' of sorts inside the round connector part of the arm. Usually if you push with the arm while prying up on the opposite edge with a flat blade screwdriver it will come right off.

It's sortof hard to describe, but it's really pretty easy when you do it. Hope that helps, or at least jogs someone else's memory that can describe it better. <img src="/forums/images/graemlins/kewl.gif" alt="" />