Welcome! This is a nicely preserved example of a WW I era N frame.
However, as stated above the only way to verify its originality is with a letter of authenticity from the SWHF:
http://www.swhistoricalfoundation.com/swhf_letter.pdf
There is conflicting information in the photos (some suggesting originality, some suggesting aftermarket modification) that only the letter will clarify. As you are apparently looking to sell (buy?) it, there would be a 300-500% difference in its value between a nice but altered .455 Mk II and an original .45 Colt. Lacking such documentation everything is pure speculation, on anyone's part.
Good luck in your decision and I hope it letters.
