Thats quite a rare book among the English-language collecting community. Are you able to provide a scan or transcript of your reference (within copyright, of course), or a more detailed description of the rifle you are enquiring about?
I'm not sure anyone is aware of a prototype 7.62mm No5 rifle bearing the designation "XIIE1", if that is what you are inferring. Although Enfield is thought to have made one or two specimens of a 7.62mm No5, I don't think there is any record of these being given any sort of official model designation.
Commercial 7.62mm conversions by Sterling are relatively common, but these do not carry a military model number.
EDIT: Just a guess, but are you referring to the "X2E1"-stamped trials FAL magazine that was used in the AustralianNo6 rifle test-beds?