I had read the first half or so of SICP before I started this project, but can't say that I really "got" it. Certainly a lot of lightbulbs had gone off, but I still had the feeling I was missing something. This project (and the two attempts that preceded it) was started with the knowledge that I didn't really know what the hell I was doing, at all. Each iteration got a little bit better and filled in more and more gaps. This is the first one that I can say is "done" in any meaningful sense, though there is a lot still to do if I ever wanted to make it useful or even reasonably performant (GC, TCO, etc...) . I fully intend to explore the concepts involved whether by implementing them into this language or by starting from scratch again, which I am definitely not above!
I agree that a lot of the mucking in this program isn't directly related to building a good scheme/lisp, but it was definitely relevant to my other main goal of becoming more proficient in C. I can report that that was a real success; I learned more about C from this than almost anything else I had done prior.
I will read that paper with interest, thank you for the link!