The D is the stamp indicating Damascus Steel.
The C is likely an inspector's or worker's stamp.
You're right about the 4 and the smaller 5... 4 lbs., 5 oz. before striking.
Do you know for a fact that the gun went back to the factory for the replacement Damascus barrels?
Are the barrels serialed to the gun?
You should really have the barrel wall thickness measured by a reputable gunsmith before you fire it.
It appears that you're missing the cocking hook and its screw...
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