The "No. 1" should not be mistaken for an earlier No. 1 rifle that was modified but rather as meaning experiment No. 1.
The bolt knob in the image is round (but I can't tell if its hollowed out). The decocker is like that found on the later MK IV and the Australian Jungle Carbine. Ditto with the front sight band. The magazines are the same too.
Suggest you get the book via interlibrary loan.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!