This was the TA-3B:
It was a Version as opposed to a Bomber. For an explanation of that and a bit more background on the TA-3B, see: http://tailspintopics.blogspot.com/2010/09/mighty-skywarrior.html
There were some notable external differences between the TA-3B and the other Versions.
The third crew position on the flight deck faced forward.
The canopy configuration was unique.
The 20 mm turret was just a sheet metal fairing with a window on its lower side for a camera to score bombing accuracy.
Rick Morgan provided pictures of a VAH-123 TA-3B with the practice-bomb dispensers on the pylons: