[NeedMoreTea]

RAF museum in Hendon has extensive archives, and holds a fair selection of squadron records, though mainly maintenance and base records I think, and a huge archive of photos and other papers. The National Archives holds most squadron operational records -- nearly all survived, so it should be relatively easy to check, and potentially get confirmation.

If you have his log book, a drop would be recorded by pilot and bomb aimer, but I'm not sure if that would be required for a gunner. Failing that if anyone in the family remembers their squadron # or plane's code (RAF were 3 letters -- 2 letter squadron code and 1 letter aircraft ID, so easy to remember and they'd usually fly the same plane each time), or has any bits with his service number, either will help narrow down an archive search and correlate with records.

The RAF museum have had several projects gathering anecdotes, and adding personal details to their formal archives, and an extensive research section.

I'm sure there's equivalents for the USAF, maybe through their museum in Dayton, OH? I'm sure both RAF and USAF museums are used to dealing with history enquiries and may be able to point you at other resources that may help.