The OP's carbine is definitely now wearing a model 1896 rifle sight. The sight-screws are incorrect replacements.
I think BAR has described a likely scenario as to why the original sight was pilfered.
A loose model 1896 carbine sight is very hard to find and will cost $500 to $600. The 1896 rifle rear-sight is common and routinely sells for $50 to $60.
Proper Kragsight-screws, original or reproduction, would look better and cost about $20.