Not a big deal for some - based on other for sale pictures, but that magazine appears to have side grooves right through to bottom edge - so that is a No. 1 magazine, not a No. 4 magazine. So correct for that rifle, I think.
Since it is a No. 1, has a specific sequence to take it down - the forearm wood must be removed before attempting to turn the big screw within the butt socket - else, if all parts in place, turning that big screw within the butt will split / break the rear end of the forearm - something to look at or check if you get it in your hand. Fore-end wood should be removed straight down - kept parallel with the barrel - do not want to pry down on the front end with the rear still in place - that likely breaks the "draws" inside top of fore-end wood. Is all hidden - no way that I know to tell condition and fit of those "draws" without dismantling that fore-arm.
When set up and properly "worn in" - those are amazing smooth and slick actions - I had one so slick, more than once I opened the bolt to ensure that a cartridge had got fed into chamber - it closed that smooth. Some people have aversion to the "#### on close" action and the two stage trigger pull. Both those features contribute a lot to the dependability of that design - alterations to either, tend to make the thing less dependable - or bring along other issues. The design is not about "quick change" magazine like a modern rifle - magazine pretty much meant to stay in rifle and NOT be removed, except for cleaning - very "flimsy" feed lips along the top of that magazine box that might need tuning for the particular bullet tip shape being used - FMJ vs Spitzer SP vs Round Nose - and then those "lips" are easily bent when inserting that magazine - so leave it in as much as possible - not generally a good plan to view it as "quick detach".
I am sure that I read that earlier versions of the rear sights had thumbscrew for windage adjustment - either was too expensive to continue making or was constantly getting loose in service - so later versions did away with that windage function. I have some of the later ones - have never handled an earlier one. Windage was "set" by drifting the front sight, then use "hold off" for wind, etc. No 1 was used by Australia (?) through WWII and into some 1960's and 1970's conficts - so those were made at Lithgow. I think also were made in India / Pakistan (RFI and POF), besides in Britain (multiple makers).
Because of the thin diameter barrel, I think the No. 1 was fairly sensitive to the bedding in the forearm - one of the changes made when it was morphed into the No. 4 - and an acquaintance has a "Heavy Barrel" version - so like a target rifle - made up by Australia Lithgow.