None of the source files have any sort of copyright attribution. I'd like to package this (very nice) engine for Debian and Ubuntu, and this is likely to cause the archive admins to reject the package.

From the "how to apply the GPL to your program" section of the GPL:
...
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.
...