It'd be benefitial if you transpiled the tools from Toybox, Ubase+Sbase and refactored the code afterwards.

That's it, have you looked into transpiling C to Zig? It could alleviate the process of porting by hand, also, give the GNU coreutils are stupidly big and non-POSIX, why are you doing the colossal effort? Isn't it better to port smaller alternatives like ubase+sbase from suckless.org ?