Ah! That's where it went Bindi! I'm pretty sure I have handled that rifle on numerous occasions. If I'm not mistaken it was Rob Hallam's & IIRC it was sold as part of the Charnwood Collection. I have 0C379, which is still a 4T, & a 12C Less Telescope Mk1* & a scoped up 14C Mk1*. Years ago I had 0C4335 which I now suspect was a possible RSAF conversion, but I let it go before I appreciated its potential significance, something I now regret.
Actually, I don't think it throws a spanner in the works. We know that before the decision to stick to BSA rifles only, a quantity of rifles from other sources was converted & went into service. Yours was probably one of those, & survived long enough to be converted into a L42A1 in the 1970's. A rare piece even amongst L42's.