When I blow up the original it seems to be a wingtip handhold or picket point, Danny. Maybe it was to help swing pupils into their park slot? As to the 'cabin heater' shroud over the exhaust, your 'iron men' would not need such luxuries but the carburettor certainly would. My money's on the carb heat for that mighty 375hp Armstrong Siddeley Cheetah radial. I always thought the cowlings looked too big for the rest of the Oxford even though it's 65 yrs since I last saw one flying (Binbrook, 1951)