Kollsman developed the periscope sextant in the late 1940s for high-speed, pressurized airplanes. It featured a small port and sextant mount in the top of the fuselage. When sights were to be taken, the periscope sextant was inserted into the mount. The tip stuck out about an inch above the skin on the airplane.
The crewman using the sextant (see HERE) would sit on the seat at the right rear of the cockpit.
The last 21 A3D (A-3B) bombers were delivered with a built-in sextant station located over the rearward facing seat (the periscope bubble is protected with a red cover).
These also had the DECM tail in lieu of the 20 mm turret.
Note that the fourth-man seat was relocated at some point.
I'm not sure that these airplanes also had the right-hand sextant position (at least one did), but for sure it was retained as a backup, at least initially, on most bombers that were retrofitted with the left-hand sextant installation.
At some point, the fourth crew seat was relocated to be over the entry/escape hatch.
I had thought that later KA-3Bs lost the right-hand sextant port but there are several examples with as well as without. The same is true for the EKA-3Bs since there was at least one with both:
What looks like a Venetian blind in the right-rear clear panel of some A3D-2 (A-3B) bomber/tankers is actually the sense antenna for the AN/ARN-59 DF system. There was a similar but much less prominent antenna in this location for the AN/ARR-15 MHF radio receiver in very early A3Ds. As to its exact configuration...
My overall post on the A3D Skywarrior, Bomber and Versions, is here: http://tailspintopics.blogspot.com/2010/09/mighty-skywarrior.html