This reminds me of a time when I sort of did the opposite: I networked a serial-only DEC PDP-11/83 running 2.11BSD using SLiRP running on a Power Mac…I want to

This reminds me of a time when I sort of did the opposite: I networked a serial-only DEC PDP-11/83 running 2.11BSD using SLiRP running on a Power Mac…I want to say 7500; what I remember is that it was one of the earliest models with PCI slots, running Yellow Dog Linux, and that I was mostly using it as a router at the time. Incidentally, does System 7.5 support AppleShare IP connections[1]? If so, Netatalk should easily build and run on Raspbian, and would allow file sharing between the SE and newer Macs with full filesystem semantics (resource forks, etc.), though, at 9600 bps, I suppose the floppy drive is faster, though, unlike floppies and floppy-compatible Mac filesystems, current Mac OS releases still happily connect to AFP file shares (over TCP/IP). Speaking of serial port speeds: at least at the software level, the "printer port" on older Macintosh models sometimes ran faster than the "modem port", so PPP over the printer port instead of the modem port might be worth trying. As serial communications on older Macs was also somewhat CPU-intensive, again speaking from decades-old memory, it might also be worth experimenting with a more lightweight protocol like SLIP instead of PPP. [1] While PPP is a layer 2 protocol that should, at least in principle, be able to carry AppleTalk traffic, and while both Linux and Netatalk, at least historically, supported the AppleTalk protocols, I'd be (pleasantly) surprised if AppleTalk-over-PPP was supported on the Mac OS end. Come to think of it, that's an interesting-if-less-than-useful question that I may just have to investigate (he wrote, as he confirmed his SheepShaver OS 9 install still works fine under Catalina).