Denis,
I was looking at your Fairbanks Morse Jack Jr page.
I currently have a Jack Jr and had another one for many years until I sold it a couple years ago.
My first one was a 1909 one which was painted red, while my current one is a couple years newer and is green.
Another difference is the plugs in the water hopper over the two valves.
On my older one, the plug had a recessed socket, while on the newer one is raised and a regular socket can be used to unscrew them.
I noticed on the engine you have pictured, that there is a third style of plug.
George