Hope there is more help on this, but its definitely an Enfield. My guess is that it is a No.1, from pics but the conclusive evidence is the stampings on the outside of the butt socket,
The No1 and the No4 have several parts differences and the magazine is one of them. Get a positive ID from a competent gunsmith who can also boresight the chamber area and bbl so you get the right magazine. The rimmed .303 Brit is a powerful cartridge ( with ballistics similar to a 30-40 Krag) and not hard to find.
