Impossible? I mean, I know AndyMark sells lots of stuff, but I didn't know they sold the Impossible as well!
In all seriousness, I think the Aztecs (157) did a timing belt drive in 2005. They may have continued doing them, but I haven't been to a regional with them since.
Cyber Blue (234) did a great bit of research on belts vs. chains that you can find on CD-Media.
Hope that helps!