...the guy I bought it from was an enthusiastic restorer...
The insides might well be reasonable, but the outside brass and iron have the look of a cleaned-up dug relic.
As for the stamping, it raises a few questions. Attached is a screenshot of a past auction from member Siegfreid on Quick Fire Auctions. Hopefully the inset image is clear, but the markings are the standard range of grenade type, manufacturer, date of manufacture, and acceptance mark.
The first orders recorded as placed outside Royal Laboratory (RL), Woolwich, were for 3,000 each from Edison and Swan (5 October 1914), Bulpitt and Sons (11 October 1914), Oliver Arc Lamp (11 October 1914), with first deliveries in November. The letters S&C do not correspond with a known manufacturer of No.1 grenades, and the typeface of the disconcertingly early 9/14 is at odds with period date stamps.
As for the stick, it varies from known originals - image of a genuine one attached. Although only a wooden or cane handle, the details of manufacture (thickness, taper, length, number of rings on the handle) were specified.