Hi rmventuri and thanks for making contact. Sorry to hear of your father and uncle's deaths.
There is a website Lost bombers and it shows that HR732 took off at 0009 on 4th December from Snaith. That ties in with Regle's report of landing back in daylight, even for early December which would therefore be at about 0830 after approx 8 and a half hours flight (I can never remember the key strokes for the half sign).
It is a pity that the mystery as to how PO Salvages wedding ring got returned as that would indicate his body at least was found, yet there appears to be no burial attributed to him. I don't know if there was a name or other specific identification on the ring, as the only other way would be for a PoW or International Red Cross to pass it on. It may be that the crew have been buried in an unidentified grave(s) as perhaps no identification available.
There may be German records on aircraft crash sites that might help locate where bombers crashed and who may have claimed it on the 4th Dec 1943 which could help locate what happened.
I'm sure all on here will do what they can, there are a number of RAF and WW2 websites where you might get further help. I'll see what I can do, but hope that's a start.