If (IF!!) the sight blade can be removed (only) by removing a windage screw, and sliding the blade out, it's the correct sight for the period. If both windage screws must be loosened substantially such that the blade can be removed by lifting it out, it isn't.
If you want to know without any messing with screws, the period correct sight carrier will have a slot running from the screw hole to the top of the carrier------and the later sight carrier won't.
All that said, a later sight (permitting lifting the blade out) can easily be installed in an earlier gun. The later sight came along in the early 1930's.
And as already noted, a gun (hand ejector) which left the factory with target sights will carry the serial number----that is any/all sights preceding the so-called micrometer adjustable (which requires no fitting).
This applies to either/any frame size.
Done and done!
Ralph Tremaine
And after sitting and staring at the pictures, it appears to be a period correct sight (for a 1917----or anything else from the earlier period).