I have written an ebuild (the equivalent to a package on Gentoo) that builds and installs a kernel for the MNT Reform 2.
You can find documentation on how to install the kernel on the MNT Reform page in the Gentoo wiki.
On the same page you can also find instructions on how to configure dracut to generate an accompanying Initrd.
The ebuild uses the patches provided by MNT, but unlike the kernel included in the official Debian image, it is not actually based on the Debian kernel sources and configuration. Instead it is based on the Gentoo-patched kernel sources and the Gentoo kernel configuration (which in turn is based on the Fedora kernel configuration).
If you’re interested in how it’s done, you can find the ebuild in my repository here: sys-kernel/mnt-reform2-kernel · master · Niklaus Hofer / mnt-reform2-overlay · GitLab