I tried finding further details for my FB.VI build, with little luck.
I have seen pics of the camera port, but the mirror was not protruding, so I guess it was internal, angled to obtain a 'strike photo' to the rear, unless it was retractable, with the camera port window / cover, but that's doubtful, and I haven't seen or heard any evidence of this.
Certainly 2 Group Mossies had the camera, used on low-level attacks, as evidenced by all the pics of attacks such as Amiens, Aarhus etc, and info received from former crews, but whether or not this was used on other units, I don't know. It wouldn't be required on Intruder or Night Fighter aircraft, so the port would likely be omitted.
I know it was definitely fitted to the Mossies on the Shell House attack, as the camera circuit was accidentally wired into the same circuit as the wing drop tanks. When the tank were jetiissoned over the Danish coast, the cameras started running, exposing all the film well before reaching Copenhagen !