Calvin appeared as a safe deposit alter ego in among the Transmogrifier Gun Alter Egos of the second Transmogrifier Gun story arc (7/4 through 7/15 1988).
Calvin turned into a safe by mistake; along with Calvin's chicken alter ego, this is additional proof that the Transmogrifier Gun's psychic trigger is somewhat unreliable. As Calvin turned into a light particle afterwards, this was most likely the form he originally opted for.
The safe deposit also supports the idea that transmogrified alter egos have unnatural capabilities: much like the flower alter ego, it was able to operate the Transmogrifier Gun without any limbs.