Have you done a search on fixyourownprinter.com's forum. They may have some helpful information. I found them useful when I was trying to keep an old TI Microlaser Plus going, until I realized my quality of life would be higher if I just dumped it and bought a more recent (used) HP laserjet with postscript, LocalTalk and Ethernet.

Darn, though. We had some investment in that ML+. Maxed out SIPP memory at 4.5 MB...