Since no Valiant Navs have responded, as a sometime AEO on Valiants I'll have a go with some help perhaps from sandym.
The CRT had some odd name like the Universal Indicator and was used for GEE 2 amongst other functions.The box above it looks like the Green Satin which I thought was usually to the left of where it's positioned. No idea of the box to its left but the GPI 4 was usually to the right of the Green Satin. Never used the sextant but on the only sortie I did over Russia to the East of the Kola Peninsular (looking for a sub) my main job was communicating in Morse with a USN P2 out of Bodø but my subsidiary job was to climb every 15 mins or so on the Plotter's table and use the periscope to see whether we were contrailing.