“retrogear” on comp.sys.apple2 has posted a screenshot of the Mark Twain ROM 03/04 that was never released, as well as comments made by David Empson from the mid-1990s.
What follows is a comp.sys.apple2 newsgroup discussion from July 8, 1995 by David Empson about an accidental buggy release of an Apple IIgs ROM 03 and analysis of the changes made before actual production. I have included the sections of the System 601 source code assembled by me which were referenced. Please excuse the rough wordwrapping here. I can provide a cleaner document if someone wants it.