George,
by 1968 in the North Island, steam freight ended on the East Coast in March 1969 and the West Coast in July 1969, except the fast Passenger Service on the East Coast 28 October 1971. The Kingston Flyer on the remnant Kingston Branch excepted.
As for dating those pictures the lower photo of Elmer Lane roundhouse was supposedly 1967, but only one I.C. loco shows and that appears to be a T
R shunting tractor. The colour picture has several D
S loco's,(0-6-0) built between '49 and '55 the last for shunting the wharves, specifically in the Sth.Is. Earlier elsewhere I had presented a photo showing the first B-B D
SC shunter being moved dead to Greymouth behind steam that was dated February 1968, and the first Ray Mathewson picture shows a D
SC.
Here's a fun fact; the NZR D
S was also built for British Rail as a S.G. shunter, class 04.