Daniel Seagraves wrote an microcode emulator in C for the Explorer I (E1) cpu. It current boots all the way to lisp. I made some changes to it to run with X11 and SDL, which makes it easier to run on most linux boxes.
Meroko is pretty fast and is reasonably stable. Bjorn and Daniel are working getting the networking going.
you run the current meroko with the disk images and hit "D" you should see a lisp herald.
A large amount of E1 documentation on bitsavers.org
... these pages (generated-with-lisp) ...