I also wonder if a SheepShaver emulator couldn't be used to connect?
This should work if your emulator can do bridged networking. QEMU on Windows makes this slightly annoying, unsure about SheepShaver.
Netatalk is probably your best choice, in terms of modern logistics.
@mactjaap is working on a neat project that combines netatalk and a couple other things in a pi or VM image that may work well, you could combine that with something like VMware Player or VirtualBox (should work in Hyper-V if you already have that) and then you can leave that VM running as a go-between.
Some more info on MacIPpi is here:
https://68kmla.org/bb/index.php?threads/the-macippi-rpi-the-macippi-concept-for-raspberry-pi.36906/
My strategy is to run
an ASIP server, which I'm also sharing. If you have a Linux box where QEMU will properly do bridged networking, you could virtualize that. Mac OS X 10.4 will also do AS
IP sharing to as old as 7.5.5 with the appropriate OpenTransport + AppleShare updates, but not to plain AppleShare over AppleTalk, which, say, system 7.1 would be expecting.
My notes on ASIP6 are here:
https://doku.stenoweb.net/doku.php?id=macdex:asip-6-guide
10.4/Intel can run in VMware, which has logistical benefits ("not have to leave a powermac G4 turned on all the time" and "not have to trust a 20+ year-old power supply"), but you can also run it on early Intel Mac minis, which you can still get cheap.
In addition to using these file servers for transitions, I save all my data on them day to day, to make using multiple systems easier and to make backups easier.
I also save full disk images of these systems (when the full disk fits in a dc6 image anyway) over the network. I've even done this over localtalk, which is slow but you don't need to mediate.
I know this is spicy but I avoid FTP whenever I can. It's annoying to deal with and only really good for
transfers whereas with AppleShare you can launch data and even programs right off the share.