Tony, your post of April 11, 2010 will make interesting reading. I didn't find it until today.
I'll go ahead and enter what I intended:
I transliterated Z-340 so that the symbols are represented by A-Z, a-z, and 0-9. And, too bad, one left over. I substituted "&" for that one. If not for the "&" a logical, if straw-grasping, assumption would be that ZK (if he did it) somehow began his work with the other 62 characters. This is easier to work with than arbitrary substitutions.
An impression I had is that the previous substitutions followed German letter frequency rather than English. That might point to an old WW2 manual or it might be too fuzzy in no more text than is available. Just an impression.
Does anyone know if the Navy Electronics Technician school was in service on Treasure Island during the murders? I believe there was a Radioman school there at the same time. Maybe a Communications Technician school, as well. Not that any more suspects are needed.