If folks are interested in Forths that are easy to adapt to new target platforms (which is a bit orthogonal from the OP’s Forth, which is more focused on simplicity from a machine abstraction perspective), then I highly recommend Retro Forth, which is made of a core of extensible C.
Retro, while nothing like a traditional Forth, is really the only Forth I use or port anymore.
I would love to see a step-by-step building up of a Forth from scratch for some environment. (Video/talking, or text tutorial.) I think that would have a lot of pedagogical value. Has anyone seen anything like that?
Jonesforth is presented in a somewhat pedagogical fashion: https://github.com/nornagon/jonesforth/blob/master/jonesforth.S
eForth (http://www.forth.org/eforth.html) is probably the best bet for simple internals of a traditional Forth.