The fact that the rifle dos not appear to ave any conversion markings, and to the best of my recollections and reading, the Sht LE MkIV .22/ Sht LE No2 MkIV rifles had new made solid barrels, not tubed, makes me think NORTHOF60 has got this right.
The rifle was likely converted commercially post service to .22 rimfire using a "Parker Rifled" tube insert. These were done for use by "Miniature Rifle Clubs". Any competent gunsmith could effect the conversion, but the muzzle stamp indicates the barrel was sleeved by AGP at least.
Would be interesting to see if the barrel is dated to the rifle build and serial numbered too...
The sight looks a bit rougher than pictures I have seen of the NZmodel, but not to be discounted... It looks to have been poorly fitted too, makes me think the rifle wasn't a trainer in NZ service... (markings on other areas might prove this assumption wrong.)
Yes, the sight was designed to give a "No4 sight picture" to an SMLE trainer.