Col.,
Perhaps the name of Lt Keefer on one of the pages is a lead? Report indeed says C-47 "76".
On a website I found that a 6th TCS (also) had crashed on 12 May 1943 "in the pass". This one other than the 21st TCS C-47 identified as 41-18661 by pacificwrecks.
Also a news report of 1943 with some further details about William's mission ("
Treachery in New Guinea") and what seem to be more correct spellings of names.
See:
http://trove.nla.gov.au/ndp/del/article/48912821
Regards,
Leendert