Bob

While anything is proverbially possible, I do not think that is factory.
The blade itself does not look factory, it doesn't fit the sight base
the way all the other factory blades fit, and the pin is too high.
On factory front target sights, the pin is about in the middle of the
sight base. This one is too close to the top, as though the
slot in the sight base is not cut deep enough.

I agree with Steve that the barrel is a proper 4" barrel from the
period, certainly before 1917. Somewhere around 1916 or so,
they changed the patent-date roll markings, so that it would fit on
top of the barrel. Prior to that point, since about 1903, with the
introduction of the shoulder on the barrel, the roll markings were put
on the side of the barrel, as those dies were too long for the top
of the barrel.

Could you get us some closer pictures of the front sight, particularly
looking into the rear of the front sight base, and also some good
side views of it ?

Regards, Mike Priwer