This is what
Perspex covers are for. Show off the innards, but keep the
 fools away from the live parts. 
 Exactly what we do every year when we show a running PDP-8/E to
 first-year CompSci students. 
 
I wan wondering just what is dangerous inside a working PDP8/e. Unless
you have the PSU removed and opened up, all the mains is totally
enclused.
Quite apart from the fact that a first year studend (particularly one in
a scientific or engineering subject) who sticks his fingers into a
working machine deserves all he gets.
-tony