If someone's looking for a more hand-holded approach for building a Lisp in C, I'd recommend: http://www.buildyourownlisp.com/
I have this page on my "TODO" list. What is your opinion about it? I see already that you are recommending it but maybe you can give some more details. Thanks in advance.
It starts you from scratch and I'd say it's well done, maybe even be overdone for Lisp. But you get a good introduction to the essentials of language implementation for more complicated languages.
Shameless self-promotion: I wrote a Lisp interpreter in a single assembly file for Raspberry Pi. It also starts from scratch at an even lower level, to the point of ignoring standard libraries.
https://github.com/marcpaq/arpilisp
I was inspired by jonesforth, which, if you haven't read it, is a beautiful piece of work.