Jeff
As a rule of thumb (but not always) the pilot, navigator, air bomber, wireless operator and one air gunner crewed up and trained as a five-man crew on medium bombers at OTU.
Once they had completed this training they moved onto a conversion unit where they were joined by a second air gunner and the flight engineer to train as a seven-man crew on heavy bombers.
I will have a look to see what documents I have relating to the loss.
Regards
Pete