One thought - it is possible that light panels from some
other model of computer, possibly not even PDP-8 related,
might be the same base PC board as the 8/S panel. DEC made
a LOT of light panels for all the CPUs and control units on
larger machines. At least some of them were made from the
same basic PCB. Not sure if the 8/S light panel had any
active circuitry on it, I'm thinking it might just be bulbs
and connectors.
Jon