I just did this last week on my 88. Take a wire coat hanger, cut it and bend 2 on the pieces into U shapes. Put one of the U's into the left side holes of the radio and the other U into the right side holes. Push the left U left and the right U right. The radio should pop out and you can now slide it out. Hope that helped
There is two small holes on each side of the factory head unit. Take something, maybe like a very small screwdriver, or a coat hanger, and try and stick it in the holes. Remember you have to have something in all four holes at the same time or it won't pop out. I learned that the hard way.