While there is lots of content out there, and apps that do fake 3d from single photos (with much the same results as fake stereo from mono in the 1980's), there didn't seem to be much info about roll your own. Well after a few hours messing about and a lot of lessons learned things are looking pretty good.
After a bit of judicious makery, here is a snapshot of the web page that displays live images from 2 webcams. This isn't proper video, this is 1 frame per second served up by motion and stuck into a single web page using some simple html that allows some tweaking. The reason for upside down and the html is all explained below. The webcams here are 2.3m apart.
Displayed on an original Nexus 7 in Google Cardboard (painlessly extended to accept the larger device), this looks pretty good, although the screen door effect is blatant.
Of course looking through 2 high magnification lenses at a phone screen 2 - 3 inches away is never going to be that wonderful, but resolution keeps improving so next year.......
Below is some detail on what I have done and how I have done it.