Looks like fancy Selous sideplates that I've seen installed on several rifles of that era. Designed to reinforce the wrist.

Like this:

http://nitroexpress.info/ezine/CptCurlFi...ChrisGibbs6.jpg

http://media.liveauctiongroup.net/i/20383/19368392_3.jpg?v=8D11C07886834B0