Ok... now that I am caffeinated and have had my morning bacon and lime-juice... here's my shot at deciphering the instruction book above. Which does mention turning the firing pin retainer 90 degrees, but doesn't explain how, what or wherefore. Also figured out why the safety is no longer working. More below. BTW, smartphone users may find these photos large. But I wanted the details visible.
Left to right. Safety switch itself. This has a cutout (see later photos) that blocks the firing pin and a 'leg' that fits into a slot on the firing pin block when engaged. Below it is the firing pin block. This carries the firing pin, the spring and the safety. It REVERSE threads into the rear of the bolt. It is not a tight fit. But is a REVERSE thread! Next is the little 'leg' that fits into the notch on the back of the bolt. Next is the sear which carries the firing pin. Then we have the firing pin and the firing pin spring (which is massive!) And I think contributes to the safety wear issue.
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Below we have the Safety itself showing the 'safety on the safety' and the tiny screw that holds this paddle in place. There is a small spring inside. I see no reason to take this apart. I used laquer thinner and WD40 to get it moving. It's in fine shape. Hanging off the safety 'axle' is the little ear that fits into the safety notch on the back of the bolt. This only allows the safety to move when the rifle is in battery with the bolt closed.
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Next we have the inside of the sear. Sorry, it's blurry. Camera only wants to focus on the matting. But you can see the 'interrupted lands and grooves' that mate with the firing pin. This is the sticky wicket in all this. The diagrams in the Mauser manual show a threaded collar at the back. So does the Numrich Arms parts site. This may have been used at one point, but on these rifles, there is no threading. It's a collar that you slide the firing pin into and turn 90 degrees. HOWEVER... because of wear (see heavy firing pin spring above) the pin itself sits in some worn spots and so won't turn 90 degrees smoothly. You have to compress the sear and 'wiggle it' in order to get it to pop out of its wear grooves. These are likely a result of the severe use these rifles no doubt took in service. Thousands of training rounds... and fielding. I doubt Mauser designed its 66 actions for this level of usage. And with the heavy spring (great lock time) comes incipient wear. I *believe* that this is what is causing the safety issues in this rifle (and I am told in many of them), which is that the wear is letting the sear move forward a few thousandths and is jamming the safety so it can't rotate smoothly into its notch. More below.
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Below is everything sort of laid out. You can see the notches in the back of the firing pin, lined up with the sear. And probably the best picture of the safety itself. You can see it's notch which clears the firing pin, but rolls into the notch (just visible at the top left of the sear) that is scalloped out to accept the barrel of the safety. It's this notch that I plan to work on with files (probably too hard) or stones in order to move it back a few thousandths and let the safety rotate smoothly. I am also going to stone some burrs off the sear itself. You can see some marks on the sear from dismantling over the ages. The two 'dots' are for a ball detente. That tiny 1mm ball goes into a hole at the back of the pin carrier block with a set screw. It was frozen into place with rust when I started this.
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Here is the ring that fits on the safety (you can also see it above, fitted into its recess just to the left of the red dot). This slips over the safety bar and is what keeps the safety from moving unless the rifle is in battery. It, too, was pretty frozen with ancient crud.
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Last, this is the safety in place. It moves freely, but won't when I reassemble with the spring. The powerful lock spring seems to have caused everything to pound its way forward and it would take only a few thousandths of wear to jam up the safety. And once it starts to burr up, all bets are off. I could actually get it to work if I really forced it backwards. So I know it 'can' engage. I just have to restore some tolerance.
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So mystery solved for now. And maybe this will help some who have one of these. Or some new guys who will find this in a search and realize that, hey, Snipers Hide is the place to go for vintage!
Any additional input is welcomed for sure! I will let you know how my machining comes out. I should be mowing today. But this is way more fun. Let the damn grass grow. I won't get a range report until my rings arrive... early this week I hope.
Cheers,
Sirhr
To be continued...
. I am grateful for everyone else as well, without you folks, I'd by eating sauerkraut and wiping my tears with a giant pretzel, 
