"The Aircraft Carrier Intrepid" by John Roberts (one of the books in the Anatomy of the Ship series from Conway has a nice series of plans for the Gallery Deck (which was immediately below the flight deck), the Focs'l Deck, and the Main (Hangar) Deck. The photos are mostly of the exterior of the Intrepid, bu there is a picture of a hole in the flight deck (caused by a Kamikaze hit) taken from the Hangar Deck that shows some of the catwalks in the Gallery Deck and the underside of the flight deck. Although the Oriskany was completed late in the program, I'm thinking that her structure was probably similar to the rest of the Essex class.
You might also want to check the website for the Office of Naval History - they have a large photo archive that might have some shots of the Gallery Deck.