Humblidge - Without wanting to impinge on the Master's territory - it looks like an early type British #4MK1 to me and the wood is really excellent, but it has probably been around the world a bit and perhaps has had some parts altered/upgraded ?
As the subject is exaustive(-ING?)I suggest the quality Skennerton Book on the 'SMLE Rifle' would make excellent reading, if you can get a copy in USA.
It is probably NOT a Lithgow(NSW) based rifle(Aussie) as they only ever made #1MK3s and they thought they were a superior rifle in accuracy and sight picture to the #4( I disagree, surely I feel in 1942 it was "needs-must") though a very (experimental) few aussie #5s ("Jungle Carbines") were made in 1945 (I am told), but they are now worth a lot of money, as are the mostly British-made sniper HTs + kits, to a smaller extent.
Mr H ...this rifle could be the start of a life-time hobby....best of luck.
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***Big Bunny***
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