Protocall Design, I don’t think I have ever disagreed with you about anything! However in this case, although the picture isn’t as hi-res as I would like, I think I agree with sndbggr1484, that appears to be the flat-top screw that typically goes in the left most/top most hole, under the top of the stock.
It seems to be sitting where a domed head screw usually sits.
Checked it and all screws are correct, picture does not do justice to this excellent condition firearm, Next to my 1958 Schwinn this is a great Christmas gift for me..........