Yes the socket is pierced at the top, centre, just below the top wall so that it can slide forward and block motion at the end of the sear nose (g1 on patent diagram). Pretty simple.

The Bar "k" must be carefully fitted, near the forward end of the bottom of the bar "k" with a pin through the action to provide a positive downwards travel stop. This cross pin is "m" on the diagram. Not all rifles I have seen fitted with the tang safety had this pin "m". Now, if the bottom of the hole pierced through the socket wall, and also the bottom of the inlet, are too low and you don't have the pin, the sear can be engaged by the safety bar but both the sear and bar will travel downwards and will at least feel mushy if the trigger is pulled, and be potentially very dangerous. I reckon the pin m is vital, and the non-pinned versions were an early variant. Yes, I have owned and seen rifles with no pin "m" and factory fitted tang safety.

The rear of the bar pivots in the tang body on a small cross-pin, and has two cams for the spring k4 to ride over, which is the main positioning locator for the safety (on/off). Location of the pin and the socket piercing were done via jigs to give repeatable tolerances, but depending on how those tolerances stacked up they sometimes still needed tweaking. Thus I've seen a number of different (original) treatments at the front end of the bar to get them working well. The bottom of some bars are filed into correct engagement, but some bars were grooved to accept the pin as a further positive location feature. Some bars needed filing there to get function, they show no groove but rather a filed-up bottom.

The bar pivots under some spring tension which is meant to be controlled by the machine screw coming up from under the bar about half way along it's length, this is just behind the forward wood screw and can be seen in the diagram. I've found the depth of the inlet for the bar is important, too - especially in rifles not fitted with pin "m". The bar is slotted for that machine screw to allow for bar travel to block or unblock the sear, obviously, and the front wood screw also passes through this slot. The bar is also curved, not flat, this can be seen in the diagrm also and is important.

The wood screws are critical, especially the rearmost, which is crazy short due to wall thickness at the top of the grip being thin from the counter-bore for the stocks through-bolt. Not much thread to hold things fast over the decades. It is important to bore that through-bolt hole as true as possible, and maintain a minimum counterbore for it so that wall thickness and screw length are maximised. Not so easy all the time, as the hole position and angle in sockets varies somewhat. Some factory rear tang screws were forced a bit shorter due to resultant wall thickness variations.....by a full thread or so, and it's these short buggers that always seem to fail. Forethought required here if making one. BSA had the dimensions down to the last beestodger in some places to get them reliable.

Toolmaking 101 to make, in difficulty, but still some time involved in them - and they must be individually fitted to each action and parts appropriately hardened.