Tom, you might want to try getting in touch with John August. He's been writing and releasing file conversion software lately. He may not have an answer about how to open your 1990 FD file on hand, but he may be able to point you toward an answer. Good luck.

PS My tech-savvy husband had this suggestion: These import Final Draft files. They may have demos. http://www.rawscripts.com/blog/Import-Final-Draft-Files http://www.trelby.org/ https://story.adobe.com/en-us/index.html