Beautiful rifle! Isn't it a little unusual to have the load information engraved on the sight like that? What are the barrel markings, what date was it rebarrel end to 303? (Initially I didn't read all the text, I was about to ask why they would do the Selous reinforcement for a 303).
Sharps-Nitro,
The Selous Plates are not to strenghen the wrist of the stock under recoil,they were to reinforce the weakest part of the stock in the event of a heavy impact (such as a fall from a horse as this was the means of transport then) they were originally made from fresh Elephant ear leather,this shrunk into place,giving the user some protection from breakage when weeks from the help of a gunsmith.
Chris.