I dont have a K 31 (Yet) but can speak of the 24 47 Yugo Mauser.
Ive got one, and its a dandy shooter, with an excelent bore.
The first thing you will have to do is order a tall front sight for it, because it will shoot at least a foot high at 100 yards if you dont change out the front sight.
8MM Surplus ammo has pretty much dried up, The Big Three of American Ammo, Remington, Winchester, and Federal all run close to $30 dollars a box unless you buy them at Gander Mountain, then they will be $40 dollars a box.
You can order Wolf and Privi Partison pretty cheap, at around $15 dollars a box, and Seller and Bellot for around $20 a Box. Or Reload, for it. Which is what i do now, because you can make your own brass from 30 06 cases, and Buy Speer 150 Grain soft point Bullets reasonably eneough.
Back to the rifle, you find that the 24 47 Yugo is built like a tank, there is nothing flimsy about this rifle at all, except one thing, the firing pin, Ive never had a problem, but it has been reported by some other shooters, that the intermediate leingth Yugo has a tendancy to break firing pins, and if you do that there is no known source anywere in the Continental United States that has a replacement, So you would have to get one made by a Gun Smith should yours ever break.
I speculate that alot of people dry fire these rifles, and break them but I have no proof. I dont dry fire mine.
Accuracy will be very good with the 24 47, I love mine, despite the many obstacles and inconviences its worth the effort.
If you order one of the Bent Bolt models from Samco they are lovely.