Hi there,
echoing Das Abteilung, it remains the case, to my best knowledge, that no-one has attempted the oft-called 'Nairn' open turret as used by the 11th Hussars in model form. Apart from that famous IWM picture featured on p89 of your Haynes book, I've only ever seen one other picture which you'll find via any search engine. You'd have to scratch-build a turret based on these two photos. Incidentally, it may have been inspired by, but is not the same as that fitted ion the Morris C9 armoured car, also used by the Hussars