Hmmm I think there is some confusion here. The No. 1 Mark V rifle was the forerunner of the No4 enfield and was a trials only model, only about 2000 being made and it has an aperture rearsight which was used on that model only.
The No5 which is erronously called the Jungle Carbine is a lightedn and shortened No4 really but real no5's are marked No5. I have seen some which looked like the No5 but were marked on the side of the action No4 Conv
Jungle carbine is not and never was an official British name.