Adam, Zork is copyrighted by Activision. The Hugo Zork you've included in your zip file even admits it is used without permission:
http://www.ifarchive.org/if-archive/...o/hugozork.hug
I'm planning on including the Colossal Cave (Advent.z5) with my Java IF Viewer, it appears to be freely available:
http://www.ifarchive.org/indexes/if-...mesXzcode.html