Easily done with a raspberry pi. Convert the serial output to RS232, and have a service that listens to the serial pins on the r-pi and translates them to a virtual mac serial port. Done.

Everything already exists at a software level --- netatalk for appletalk, the serial port driver for a real mac serial port, and of course linux on the r-pi. The only part needed is gluecode to convert the RS232 signals to a virtual localtalk port

That part is easy --- question is....is it cheating (too easy?)