It's tricky to get the reflector off without cracking it (ask me how I know). On the back, it should have 10 of these protruding plastic stem-like things (see image below):
They are press-fitted into 10 metal clips, which are in turn press-fitted into the sheet metal. At least on my '84, the screws at the end of the stems are not used. The clips have a death grip (I mean, a real death grip) on the plastic stems. You can't be too careful in prying the reflector out of the clips. Even then, there's a good chance you'll crack it. A new reflector is around $600 - good incentive to exercise care.