I wonder if you could convince the mac there was was a postscript printer on the other end, then retrieve the text from the ps commands that were sent.
/? farallon Mac serial port Ethernet
https://www.google.com/search?q=farallon+mac+serial+port+eth... : $50 and no FreePPP or Zmodem or AppleScript serial port to a [soldered] cable to an Arduino/RP2040W/ESP32 (which is probably faster than the old Mac).