I think the NMM Library at Beaulieu may still have driver's handbooks..they sent me years ago a copy of a 1940 COE cab layout drawing from a book that must have been one supplied to GM Ltd or Vauxhalls when new as part of the dollar purchase for books and parts for the ex-French diverted contracts.
Or post a note on this forum as the cabs should be the same as the civvy version:
http://oldgmctrucks.infopop.cc/eve