I have just safely received this from @XTiffy - the fence securing screw is the shiny nickel plated screw you can see in one of the 4 small holes on the top of the plate - it is just stored there and would be screwed from underneath to secure the fence in one of the 4 holes. It also has the washer that is missing on mine!I have just sold a Stanley 71 on this forum (when I have confirmation of receipt I will take it down!). I would buy at that price, I had mine from new and I can't remember ever using the fence. I sold it complete with that missing bolt, which if you look at my photo is a plated raised head countersunk bolt. These should not be difficult to find, especially as a member has offered you one. The thread is likely the same as the thumb screws that hold the cutters, depth stop etc.
Glad the plane looks complete, good luck getting it!This is mine and looks like I paid £18:52 for it. The screw that holds the fence is missing on mine to but that will be my fault.
View attachment 196758
View attachment 196759
View attachment 196760
View attachment 196761
View attachment 196774