What Sly said. It would definitely be interesting to know if the driver side panel fits a pre-'90 box. The steering column changed considerably in '90 but maybe the panel would fit the pre-'90 boxes. I don't think that panel changed much after '90 all the way through the end. That panel I think would only be an aesthetic upgrade if it fits.
The clip Sly mentioned, again from the heater core writeup.
Panel off:
Panel on:
Upper support for that panel is a bolted in brace piece:
That brace can be removed with the panel still attached:
I don't have a good shot of that panel though.