Looking for info on the extended features of the SWIM? Look here! This should really cover every additional feature you need to know to reimplement it, then it’s just a matter of connecting the hardware and software together.
20201026/https://web.archive.org/web/20131106030115/https://dec8.info/Apple/Apple%20Floppy%20Notes/SWIM%20Chip%20User’s%20Ref.pdf
I found this from a link to a Macintosh Portable schematics reverse engineering project, here:
20201026/https://github.com/ppieczul/macintosh-portable