From the photo, the 'butt can' normally found on the end of the boom is not mounted in this photo, as the MAD gear was only there for show with VC-920. Here is an additional photo of VC-920 Avenger 906 showing the 2 'butt cans' (transmitter & receiver), as well as the wing-mounted radar and rocket rails. The port wing has four rocket rails, while the starboard only three. One was eliminated due to the proximity of the radar pod.
The 900 numbers were changed between aircraft as the Avengers were back and forth with Station Shearwater. They were strictly squadron numbers and nothing to do with the aircraft serial. My aircraft was always 905, although I can remember at least four different aircraft wearing that same number."