The 89-93 should all be the same. The 94+ have a solid curve along the window portion, and the earlier ones have the raised parts on each corner.
I have a 91 Bird with no wiper cowl at the moment .. im working on making a fiberglass cowl to replace it since I dont have wipers or anything else ...
But I did try to bolt up a 94 cowl at one point and the mounting points were in different locations. One or two screws would line up, but the rest wouldnt.
The bottom halves are slightly different also, but not really, but I think the bolt holes are in different spots .. you could just drill new holes in the lower portion to match it up. I think it would be possible to use the lower halves with a different upper half if you could figure out what to do with the mounting points. They are just held together by the weatherstripping anyways.
- Dan