I would date the gun at 1894 - the 1897 would correspond to records after Webley became part of the operation. the Patent Gas Check (patent 617 of 1882) is what you are seeing as 'O' rings around the pins and the windows are Scott's Crystal Cocking indicators (patent 3223 of 1875).
The gun has obviously been reproofed in some way after 1955, the decimal 736/737 etc only came in to use after that year. You need to post good close ups of all the proof marks to get a clear indication of what work was done. Possibly the gun was reproofed for B.P.only
