Heh, yeah, I said at the start of my last comment that I must have missed something… and I sure did!
Ok, for this sort of Chrome control I usually turn to an extension from the Chrome Store.
(We have done this in the past with rotating Chrome tabs; see our post about that here; Rotating Groov Pages (Tabs) - #2 by Beno)
In your case Thom, have you looked at this guy?
https://chrome.google.com/webstore/detail/multi-screen-presentation/hdcpaafhapbbddofomepnhhdfcpikdnf?hl=en
This extension automatically opens the appropriate number of browser windows to the specified URLs and sets them to full-screen in the appropriate monitors.
Seems to match pretty close to what you are needing?