Shovel - I can not answer all your questions - maybe some - I would say that is a "Large Ring" mauser - that front ring should be circa 1.4" diameter or so - versus 1.3" for a Small Ring Mauser - is up to you to look inside to see if it is a "C" bulkhead in there, or an "H" bulkhead.
I would say that was a military stock at one time - where it was cut off at the front, you can see the hole where the cleaning rod had been inserted - will be or used to be a metal "ferrule" just ahead of the recoil lug inlet - within that wood stock - is what the inside end of the cleaning rod turned into so it would not fall out of the rifle.
The sling for that rifle likely was on the side - so a buckle or loop through the butt of the stock (not too far from the wrist), and then the band near the front often had a sling loop to that side.
It appears to still have a military rear sight, but the hand guard and those bands are gone - I can not make out if that is a military front sight, if the barrel was shortened and re-crowned, or whatever - I believe the Israeli conversions to 7.62 NATO precisely matched the 8x57js barrels that they removed - but I could be corrected about that .
From the grain that I see on that stock - I will take wild guess that is a laminate stock - not a solid piece of wood - but is only a guess. I would need to see better for that bolt - is at least one here that someone "modified" and allowed the rear of the bolt body to get MUCH too hot - I would guess was done without heat sink or heat stop paste - that softens the cocking cam, so it can gall or wear in a short time. Often that same lack of attention mungs up the buttress threads within that bolt body and makes the shroud hard to turn - which makes cycling the bolt harder than it should be to do. Brownells sold all the necessary parts and supplies to make those bolts to be "scope friendly" - but apparently some did not see the need for them.
I believe that version of "cupped butt plate" may have had a disassembly hole - was a WWI thing that most soldiers knew how to dismantle their rifle - Canada, Britain, Germany, USA - so once that firing pin assembly is screwed out of the bolt, the firing pin tip was inserted into that hole - the shroud pushed down and the unit was completely dismantled to pieces - similar to P14 and M1917 and others of that time. There was some Mausers (earlier I think) that had a "button" on the side of the butt stock for the same purpose as the hole in the "cupped" butt plate.
Your picture shows someone replaced the original 3 position Mauser safety with an "up / down" two position safety - by doing that, they altered the dismantling procedure for that bolt - to get the firing pin out - can still be done, but not as per WWI system.
The follower in that magazine likely had a right angle stop - to prevent a soldier from closing the bolt when his magazine was empty - would have allowed him to think he had a round chambered when there was nothing in there. For some reason, was a thing when sporterizing those rifles for hunting, to grind that shoulder off - which allows the bolt to close on an empty magazine, without depressing the follower. I am not sure that I understand why that was thought to be a desirable thing to do for a hunting rifle, unless that is what the customers wanted??
If the ONLY alteration done to the floor plate was to add that button - then depress it - push towards the receiver, and at same time slide the floor plate maybe 6 mm towards the trigger guard loop - the floor plate, magazine spring and follower will fall out into your hand. If a hinge was added at the front of that floor plate, and if the stock was relieved for clearance, that floor plate would hinge open. Is a broken one here - someone epoxy bedded the receiver and epoxied the magazine wall to the stock - and there was no clearance for that hinge to pivot - someone forced it to open - the epoxy held, so the magazine box broke in two.
An original military extractor will NOT allow you to insert a single round into the chamber and close the bolt. Was many extractors that were modified to "jump over" the rim of a chambered round, so can do so - but I do not know of any military that did so, or any mil-surp replacements that were "pre-ground. Is likely worth your while to find out if yours will single feed or if it won't. The original Mauser 98 design required a single round to be snapped into the magazine, and THEN the bolt to be closed, chambering that round coming up underneath that extractor..