Steve, it may not get you any further, but here is the RAF Loss Card link giving some further details of the crew, equipment and take off time for JA696, which you may not have seen.
http://www.lancasterbombers.net/Loss_Cards/1943/Sept_43/Sept_43_Pt1/files/book.swfJohn is shown as being the mid upper gunner.
100 squadron also lost JA630 that night. The bomb aimer in that crew DOES have a known grave, yet all other members of BOTH crews are on Runnymede.
HARRILL, EDWARD CHARLES. Rank: Pilot Officer. Trade: Air Bomber. Service No: 157285. Date of Death: 04/09/1943. Age: 28
Regiment/Service: Royal Air Force Volunteer Reserve. 100 Sqdn.
Grave Reference: 1. K. 17. Cemetery: BERLIN 1939-1945 WAR CEMETERY
Additional Information: Son of Edgar George Collins Harrill and Edith Ella Harrill, of Cheddar, Somerset.
Their Loss Card seems to note that he was buried in Heerstrasse BMC. Plot 1, Row K. Grave 17.
John King was also identified, together with 4 unknowns, yet he is on Runnymede, so perhaps you might be able to pass this information on to 100 Squadron.
It could be that the JA930 crew might yet be identified if CWGC can advise if Harrill had any other related burials. It looks as if Heerstrasse was the original name for Reichswald, as the grave information is identical. If there are "Known Unto God" headstones around him, that suggests they are the rest of his crew.
KING, JOHN. Rank: Sergeant. Trade: W/Op. Service No: 1128416. Date of Death: 04/09/1943. Age: 30.
Regiment/Service: Royal Air Force Volunteer Reserve. 100 Sqdn.
Panel Reference: Panel 155. Memorial: RUNNYMEDE MEMORIAL
Additional Information: Son of William and Winifred King; husband of Mary Catherine King, of Skipton, Yorkshire.
Sorry, doesn't really get you much further, but another (small) part of the jigsaw.