Keeping up with the slew of file suffixes used by IF systems is probably going to be a full-time job. Unfortunately, it's also necessary -- we can't have binary file formats served as text/plain.
Here is the .htaccess file that is used by this web server. It covers all the file suffixes I could find in the archive, as of this date.
Most of the wacky file formats are just application/octet-stream. I do have special handling for Z-code and TADS game files, since they're so common. These are application/x-zmachine and application/x-tads, respectively. Not so common, but dear to mine heart, are application/x-glulx and application/x-blorb. By popular request I've added the TADS-3 type, application/x-t3vm-image, as well.
If you have any comments, complaints, or suggestions, please send them to <tech .at. ifarchive .dot. org>.