Looks to me like the mount in the dovetail is a genuine Stith and the rear ‘mount’ is something that was fabricated by the owner or a gunsmith. How is the scope attached to the rear mount?
That is the correct Stith mount for these rifles, the rear uses two holes for #6-48 screws and can directly mount on later version of these rifles that were drilled & tapped for the No 15 receiver sight. The rear mount is not long enough for to use the early hole pattern for the No 5 & No 10 sights, those used two different size screws spaced farther apart - one a #10 & one a #5. There are a couple members who have these mounts. The examples I have use slot heads screws, which is what the early Stiths used. later they went to all socket heads.
Here's an example I have that was taken off a gun, who ever did it, did not remove the front tube from the dovetail piece so they could loosen the set screw and just drove it out, which left a lot of marks & distortion and I would think a big groove in the bottom of the dovetail on the gun. This one uses all slot head screws except the ones holding the front tube to the dovetail piece.