Note that when these kits were prepared, Diffutils 2.8.7 was a "test release", "which should not be used in production". On the other hand, in Diffutils 2.8.1 (which was an official release), the "diff" option "--ignore-file-name-case" did not work properly, and that problem seems to have been solved in Diffutils 2.8.7. (Some GNU/Linux distributions also appear to include Diffutils 2.8.7, so it must be good.)
/ftp/diffutils/diffutils-2_8_7b_vms/vms_notes.txt
/ftp/diffutils/diffutils-2_8_7b_vms/diffutils-2_8_7b_src.zip
/ftp/diffutils/diffutils-2_8_7b_vms/diffutils-2_8_7b_vms.zip
The Zip archives for these kits were created using the Zip "-V" option to preserve the VMS file attributes, but the source files in these Zip archives should be usable on a non-VMS system. The VMS port notes mentioned above (and included in the kit) describe how to restore the original mixed-case and/or multi-dot file names in the kit which have been altered to accomodate the more limited VMS ODS2 file system where this work was done.
All versions of GNU Diffutils for VMS, including older and experimental ones, may be found at the archive: /ftp/diffutils/
FTP access is also available at: ftp://ftp.antinode.info/diffutils/