"Rifle Factory Ishapore" before 1902 it was Powder Factory Ishapur (it was anglicized to Ishapore). In 1902 construction was undertaken to convert it to a Royal Ordnance Factory (ROF) that work was finished in 1905. First use of the RFI mark was on converted rifles (MLEs converted The SMLE Mk.I* I.P.) that were built during the years 1909-1914. Ishapore is still running and currently makeing the 5.56mm INSAS weapons system for the Indian Army.

155 would be an inspector number.

Welcome PJ and I'm sorry.... you are already showing the first signs of an Enfield infection, collecting the original accessories for it. It only gets worse from here
Welcome and hope you enjoy your new hobbie.