Just wondering how you had narrowed it down to Lemke shooting down F/L Henderson. Four Spitfires were claimed in the period 09.26 - 09.45: two by Lemke, one by I./JG 2's Hptm. Adalbert Sommer and one by Ofw. Franz Malsch of I./JG 4 (5km West of Cori). Only Henderson's aircraft was lost however.
601's ORB mentions only that Henderson "did not see 2 E/A which appeared behind him", not specifying whether these were Bf 109s or Fw 190s.
If you've got more on this action, I'm interested, having done some work on it myself. See:
http://www.ghostbombers.com/JG2/jg2frame.html
http://www.ghostbombers.com/JG2/7marchcl.html
http://www.ghostbombers.com/JG2/601.html
Have you tried the Ministry of Defence's Air Historical Branch? They were very helpful to me over a report on a crashed Mosquito and its crew in Italy, found after the Allies occupied the relevant area in 1945.