I would wait for Craig Barry or Lanyard Puller to weigh in, something doesn't quite ring true on the pictured rifle. Most, if not all, P56 were iron mounted. The middle picture is a P56, the top picture is a brass mounted P56 Sea Service rifle neither of which had the sling swivel on the trigger guard. The bottom picture is a P58 Sgt's Fusil over an early Parker Hale P58 Naval Rifle which is a superb reproduction of the original. I think what you have is a P58 Naval Rifle. If that JS anchor is legit you have a real gem but I suspect it's a stamping closer to 1961 than 1861. Looking at it with my jaded eye I think you have a legit P58 but I see no evidence of US/CS service either way. I don't believe it is a put together either as these were hand made and the fit and finish isn't sloppy or mismatched like I have seen of many put togethers. Also I see no evidence that this is a Khyber put together. In short you have a nice piece.
Lodgewood has both a ramrod and rear sling swivel if you wish to return her to service.
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