I was reading this with some interest, specifically the debate over when the glass rear light with separate reflector changed over to the larger plastic lensed unit with integrated reflector.
My car was registered towards the end of 1959 according to my V5 document. It was a LHD super plus, with the large 7" headlamps and separate pod lights, with the cow catcher bumpers and also had the smaller side aluminium trim of the earlier cars. However it had the 3" plastic lensed rear lights. Lee Turnham of the IOC insisted that this was not original equipment for a pre 1960 car, and that they must have been retrofitted. I considered this wasn't impossible, my car being originally festooned with lights and mirrors (I think a previous owner must have watched Quadrophenia one too many times) however I could never find any sign of holes in the body where the fixing screws for separate reflectors would have been mounted, and there was no sign of filler or welding of said holes either.
Therefore I came to the conclusion that the crossover occurred sometime in mid to late 1959.