Welcome! A great quest - I think a challenging one. I'd recommend reaching out elsewhere too, if you haven't already: vcfed forums, classiccmp mailling list, retrocomputing stackexchange, Computer History Museum, Living Computers Museum, and so on.
I vaguely remembered something, and there are a few links within, but it's not quite what you seek:
from 1983: 6502 assembler with Lisp syntaxalso maybe some pointers within
The COMFY 6502 CompilerPlease share any findings!
Edit: a list here with many cross-assemblers but none of them, I think, old enough
https://telarity.com/~dan/cbm/cross-development.htmlEdit: BDD offers
this mid-70s personal experience:
Quote:
Before any programming could be done, an assembler was needed. MOS Technology had a reference assembler that could run on some systems, but not on the IBM 370 mainframe that we had at the time. So one of our staff programmers studied the 6502 data sheet and wrote an assembler in FORTRAN, which worked well and was pretty fast.