I think Time Traveller used a primitive HUD type technology that basically projected a flat image onto glass. I don't think the projections themselves were recorded stereoscopically and they definitely weren't 3D rendered.

Okay, the Wiki site explains: "The holographic effect is an optical illusion using a huge curved mirror and a CRT television set." so it definitely wasn't a holographic projection.

The same Time Traveller effect can be seen in those novelty "mirror" bowls that you place objects in and the curved reflective surface on the inside makes the object look as though it is "hovering" near the opening of the bowl (which is narrower at the top to limit viewer perspective). Neat illusion, but hardly the same.

That's pretty much how I would have done it except you can only fit so many heads in an arcade cabinet.