Glenn,
Rifle number 745 has no despatch information recorded so it is therefore very likely to be one of the rifles assembled by Charnwood Ordnance. Charnwoods purchased an unknown number of receivers / barrels / woodwork etc from Enfield at the end of their production run and assembled them at a later date.
AlanDeEnfield may be able to shed a little more light on it for you.
Cheers,
Simon.