Man that's alot of rapid fire questions! It took all day for me to figgure out what yer askin. I'll try ta answer some.
#1,,most, the tang screw goes through the stock at the head of the grip and attaches through the stock to trigger plate(not the trigger guard), this is sometimes called the button screw( or to "button up") T/C adds the smaller wood screw to the rear of the tang to add accessories.
#2,, no,, the brunt of pressure is on the breech. The "tang" just holds the breech in place against the stock, the motion of Newtons 3rd law forces the energy back and not up against the stock and then the shoulder.aka:kick/flinch maker
#3,, I think your talking about the lock screw? a small fracture here won't affect shooting ability much,,as long as the lock itself is seated properly in it's inlet and held in place (don't over tighten!!) and you have the wedge key in place and do all the other stuff,,
Is it safe too shoot? I cain't answer that!! but I'd guess the dealer wouldn't sell it if it wasn't!