For the Swede you will find a lot of information here:
http://gotavapen.se/index_eng2g.htm
Check out the pages 'Swedish Military Rifles 1894 - 1960', 'FAQ about Swedish Mausers' and 'The Swedish inspectors codes for Swedish Military small arms.'
I believe that the threaded barrel has been done post-ww2 during refurbishments from what I recall reading. It serves, as others said, to attach the debris-catcher for wooden bullets. You will find images of that on the site I liked above.
Concerning the wood, there is a lot of variability going on, as the swedes started out using imported wood from France I believe. When WW1 started that supply was cut off and they mounted their rifles in beech I believe. So the early production M96 rifles often have much nicer wood than those made during and after WW1.
Check out the C&Rsenal video on the M96 on YouTube, too.
Edit: for ammo, PPU makes good quality and cheap rounds. You may want to try the 120 grain HPBT or the 139gr SP. Barrel twist should allow you to shoot up to 160 grain rounds (twist is 1 turn in 200mm from memory). 6.5x55 is nice to reload too, as you have plenty of choice thanks to the 6.5 creedmore hype. Look for slow powders (in europe that is vihtavuori n150 to n165, depending on the bullet).
Edit 2: obvious point, but just to be sure: 6.5x55 has two pressure ratings (like 223 and 5.56 nato do): 6.5x55 SE or Swedish Mauser and 6.5x55 SKAN. The former is safe in old guns. The letter has significantly higher pressures and is meant for modern rifles (Tikka, Sako, Sig STR etc.). The PPU I mentioned are safe. Caution with hunting ammo, that may be loaded to modern specs (Norma ammo for example). Pay attention to this when you reload, too, there are two tables for this caliber.
Great find, I am envious of that Swede!