There is a picture of one on page 46 of the RSTS Professional
v4n4 (Aug 82) taken before an internal DECUS meeting.
I'm pretty sure there is a plex at CHM as well. They have a
collection of several dozen unusual DEC front panel plastics,
including one for a 32 bit machine that looks like it would
be for a 360 architecture.
No one has ever been able to identify what THAT was for.