The fittings for the the sling in the first photos are British.
To date I haven't seen N/|\Z marked L1A1 slings. Plenty of Australian, Canadian (No.4,Mk1) and WW1 dated slings in the past and some British Slings in the Ancillary Packs, brand new dated 1963/4, but none of them NZ marked.
How clear are the markings on yours John? What is the small wording perpendicular to the N/|\Z
New Zealand stopped marking rifles NZ in 1960, I can't see why they would bother to mark slings, unless it was applied by the manufacture for some reason?.
The marking doesn't match the earlier N/|\Z marked .303 slings as they have Serifs on the letters
Hi Kev, mine is NZ 1943, I assume it started life on a lend lease No4 MK1*.
.303, helping Englishmen express their feelings since 1889