I know you must be frustrated. Like psfred, I cannot remember for sure if there were screws but there were lots of clips. There may have been screws, too, but you should be able to see them. I know there were a few screws but I can't remember if they held the top on. I remember thinking that the heater core could be replaced without removing the box from the car, when I had mine out to do the evaporator.
Some of the pods/linkage will probablt have to be removed before the top will come off, too.
Good luck! Keep us posted.
I just found this photo of the top off: There are some other pics there, too:
http://www.w124performance.com/images/W124_dash/
