Here's 2 pages taken from the ".303 Rifle, No.5 Mk I, Parts Identification & Lists, No. 5 Series Notes, Exploded Parts Drawings, Descriptions, Accessories & Fittings" by Ian Skennerton.

As far as the fore end metal cap...all I can extrapolate from Alan M. Petrillo's "The Number 5 Jungle Carbine" is that they started manufacturing them with the metal cap in late 1945 or early 1946?

---