More '633 Squadron' film queries

I am continuing my research for my forthcoming book on aviation films. Some further queries – in his book ‘Flying Film Stars’ Mark Ashley lists the pilots who flew the Mossies in ‘633 Squadron.’His list includes Martin Caidin and Neil Williams. However in his autobiographical book ‘Airborne’ Williams implies that the first time he ever flew a Mosquito was when he piloted TA634 from Speke to Bovingdon in 1968 for the film ‘Mosquito Squadron.’ So who is wrong and who is right?

Also where exactly was the ‘pre – credits’ sequence with the Miles Messenger filmed? Also two German armoured cars appear in the film. One is an Alvis Saracen but the other one is obviously a mock up . What vehicle was used for the conversion. Was it a Daimler Dingo or Ferret or a Humber armoured car or what?