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?
"When the going gets weird, the weird turn pro." Hunter S. Thompson
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.