Interesting item. I saw it around the back at Duxford years ago. Major Picton was the gunnery trials officer at Shoeburyness who used it as a mobile office, and the logo "Major Picton's Palace" was painted on the back, (front??). There was a large hatch in the superstructure at the rear, and a set of steps to gain access to the inside. The driver sat up high to the side of the gun, and apparently this was a good driving position. I can't find any reference to a Conq gearbox, so perhaps I thought wrong. Perhaps SteveO can help.