It appears the MCS-4 project download link on the OpenCores site points to a tarball created in 2019. I've emailed the OpenCores site maintainers to alert them, but I don't know how long it will take them to correct the problem.
In the meantime, I've created my own tarball of these sources and placed it on Google Drive:Download link: mcs-4_20220103.tar.gz
File size: 1456944 bytes
MD5 checksum: e2ee2aa03b7dfefd5f10d3e2a6323889
