It probably won't help your research much, but I've got an entry in my log-book;
2nd June 1965 Shackleton MR2 WR 961 Take-off 13.15 Land 23.45. Duty - "Search and rescue for 39 squadron Canberra. Nothing seen"
If my memory is correct, the Canberra detail was a training one which included "recovery from un-usual attitudes" which was part of the recurrent crew training syllabus (No simulators to practice the dangerous bits in those days). I believe the rumour at the time was that they lost control and spun in..............can't remember if any wreckage was ever found ?
Hope this helps ?