I’m in the lucky position to own the last offically released software package for the DSM860 cards.
That said, it’s a mishmash of different tools, code and compilers not always compatible with the different boards (860/8, 860/16 and 860/32). Still the sources and specifically the assembler and C compiler may be helpful for a kickstart.
I’ve adjusted the installer to create a single-install instead of the original 3 floppies installation. See the readme.txt file for more details.
And if you’re interested, here is the the source & binaries for my Mandelbrot example.