MacFarlane's book (p106) contains an organisation diagram. Captain DR Eden is shown as "Director of Flight Operations". Below him is Captain PA Grundy, who is shown as "Flight Operations Manager". Captain IH Gemmell is below Capt. Grundy, listed at "Flight Manager - Technical".
My understanding is that the Director of Flight Operations job was 100% office, while the rest of the exec jobs were part flying / part office.
The "Chief Pilot" title might have had more to do with seniority: It looks as if Capt. Gemmell had been with AirNZ since the 1940s.
The two execs that Mahon describes in his book are Capts. Gemmell and Grundy.
Yes, I've seen the diagram you're referring to.
Initilally I thought that you were joking with your 1940's date. But in the Royal Commission video, Captain Gemmell appears as if he's in his mid-late 50's. If he started flying in his early 20's or late teens, then he would have commenced his flying career in the 1940's as you suggested. I also note that there is a reference to him as General Manager Airline Operations for Polynesian Airlines as recent as Sep 2003, which would hve made him probably in his mid-late 70's when still at that airline.