Not sure if it is an intended part of the model, but to my eye, while inspecting the scope model in in-game inventory, it seems that at the attaching part of the scope the rail itself that the scope would normally be attached to in a modern AR-15 like weapon, for instance, is already there.
Now I'm thinking maybe it has been modeled there on purpose, explains why it could possibly be mounted on a Mosin, so
Maybe add some kind of extra item into the game, that would allow the mounting of rail type attachments, LRS included, into Mosin and perhaps other future firearms. To my mind, finding a scope mounted on a seperate part of mounting rail... is just no.