@aeva Good luck! (Let me know if you want any advice, I like talking about Gentoo, I don't know whether you've installed Gentoo before or not and I don't want to be condescending by explaining things that you already know)
In case it helps, I followed this article to set up building binary packages on the faster machine and installing them on the slower machine: https://wiki.gentoo.org/wiki/Gentoo_Binary_Host_Quickstart
Problem is that that requires an existing Gentoo machine, though... Or doing some stuff with Docker on a machine that runs some other distro, I guess
But compiling on a Core 2 Duo itself is 100% possible if you're OK with letting big compiles (like Clang and GCC) run overnight