Agreed that the rear air circulation is uninspiring to say the least but the deck vents do exit air to the outside world, but not any huge quantities from my observation.
My plan is to us the 47 style NACA ducts. I've calculated the area of one duct to be more than adequate to feed the carbs at standstill. At speed it'll flow more and I'll incorporate an air bleed within the engine compartment so as not to be force feeding the induction system. I intend to incorporate a flat panel paper filter using a housing from a common vehicle or make a fibreglass box to suit the same filter.
Hopefully I'll have most of this tucked up under the RH sail panel and connect a normal flexible duct to the air box. I figure that's perhaps the only place available to get ambient air that's relatively free of dust.
The LH duct? - dunno but I'll likely leave it free and let it contribute whatever to the engine bay air circulation.