All source codes are from Index of /Archive/Distributions/Research/Dennis_v6 as follows.
# download source codes
wget https://minnie.tuhs.org/Archive/Distributions/Research/Dennis_v6/v6root.tar.gz
wget https://minnie.tuhs.org/Archive/Distributions/Research/Dennis_v6/v6src.tar.gz
# extract files
mkdir v6root
tar -C v6root -xzf v6root.tar.gz
tar -C v6root/usr/source -xzf v6src.tar.gz
# relocate source codes
mkdir sys source
cp -r v6root/usr/sys/ sys
cp -r v6root/usr/source/ source
# delete unnecessary files
rm -f v6root.tar.gz v6src.tar.gz- v6root: root directory
- source: copied from v6root/usr/source
- sys: copied from v6root/usr/sys