As far as I remember there wasn´t much difference between 1.3 and 1.2 except that 1.3 could boot from HD. But if you want to play and Infocom game, why don´t you use any of the free zPlayer implementations like "Amiga Infocom" by InfoTaskForce/David Kinder, which also works under Workbench 3?
1.3 was a quick fix to get Automount in place for HD, IIRC it was otherwise identical to 1.2... I think it was Dave Haynie who explained that in an interview somewhere.
