You can run Empire on a PDP-10:
https://github.com/paulnank/nankervis-pdp10-js/issues/1#issu...
Yes, I've seen the sources that say it never was stable, but I assume that at least what's in the recorded demo was at some point possible to run; of course it might be coming from a long-lost source/or binary.
See this for some more information: https://github.com/PDP-10/its/issues/425#issuecomment-145588...