On the subject of emulators that would actually run on 68k machines: There's a pretty good TRS-80 Model I emulator:

http://yves.lempereur.name/trs80.html

I've never used it on real hardware but I did play with it under BasiliskII on a setup which was only about as fast as, I dunno, an LCIII and it ran okay.

Note of course that a Model I is a *2 Mhz* Z-80 with much simpler hardware than a Gameboy. So it's no surprise that it's a lower bar to clear when it comes to emulation.