Dave,
If he was in the RCAF and flying on Halifaxes he could have been with a Canadian or British squadron. There was no 31st Bomber Group there was 1,2,3,4,5,6,8 and 100 Groups.
see thsi link on my site for the squadrons which made up ther various groups this may help you find the base he was at. Perhaps it was 431 squadron they operated from North Yorkshire out of Croft.
http://www.bombercrew.com/groups.htm
I believe that what he said about the navigators on US bombers is correct, if my memory serves correctly they operated with a "Lead Navigator" or somethign to that effect.
A good book that covers the bombing campaign and the differences between the USAAF and RAF Bomber Command is the The Bomber War by Robin Neillands.
HTH.
Matt
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Remembering those that served in Bomber Command!
www.bombercrew.com