This seems like it is installing scripts, maybe you should use INSTALL_SCRIPT. Also, I am not sure there is a point of installing the Linux related scripts.
Never, never, never, never, use cp to install files in STAGEDIR.
No, I checked scripts and they are meant to be Bourne shell.
However, shellcheck finds some errors in them. I asked upstream to correct and create a release.
IMO, it will be reasonable to wait a few days in a hope that they will respond.
These are for Linux file systems, not for Linux itself. They allow to manage Linux filesystems like ext2.