I don't know the answer to your question specifically, but I will note that my Kyocera Color Laser Printer with Postscript prints fine from OS 9.x but not from my installation of OS 8.x.

I suspect that a newer version of the LaserWriter Driver (extension) is needed. So that may be your need. See if the LaserWriter extension in your 7.6 installation is particularly old.

Of course, the LaserJet 4M is ancient, so it can't require especially modern Mac extensions.

You might just try a google search on *LaserJet 4M Macintosh system requirements* and see what comes up. Oh, you may wish to throw jetdirect into that search as well...