Nice find. My father was an observer (waist gunner) on a B-29 and I'd never heard of Weaponeer until now. Looks like it was only on the 29's that delivered the atomic bombs, per that Howlett Interiors publication, herewith:
"Weaponeer's Station Above: Definitely a Silverplate only device. The Weaponeer's Flight Test Box (FTB) as fitted to Enola Gay. (Scott Willey) The FTB for the atomic bomb was installed on what had been the forward end of the radio operator's table in standard B-29s. Cables from this box ran through the pressure bulkhead and connected to the top of the nuclear weapon. The weaponeer, a Silverplate only crewmember, could monitor the condition of the batteries and the various circuits in the bomb. The box above is not the box that was in Enola Gay on 6 August 1945 but an updated one installed for the Crossroad atomic tests at Bikini Atoll in 1946. The original (pictured right – Mike Hanz) has disappeared, probably when the Crossroad's box was installed. "