This might be of interest - it's portable, by intent, rather than being 6502 specific.
Here's documentation in PDF format.
Here's a home page.
Although the central VM is written in C, I see it's buildable with TinyCC, and there's a barebones version, so I hope it's not too large for our world. In any case, perhaps there are some nice ideas within which can be borrowed.
Quote:
RETRO is a clean, elegant, and pragmatic dialect of Forth. It provides a simple alternative for those willing to make a break from legacy systems.
The language draws influences from many sources including traditional Forth systems, cmForth, colorForth, Factor, and Parable. It was designed to be easy to grasp and adapt to specific uses.
The basic language is very portable. It runs on a tiny virtual machine (Nga), which is written in C. There are multiple interface options, the main one (rre) is buildable with just the standard C compiler and libraries on most systems.
(via
here and
here)