The additional pics of the stock where it meets the frame show that it isn't near as bad as many old Lefever guns. Those "fingers" above and below the sideplates are a fragile area, and many old original Lefever stocks have bad cracks, missing splinters of wood, or crude repairs. That area is one of the weak points of Lefever shotguns, and probably accounts for most that have had or need stock replacements. A combination of thin areas of old wood and heavy recoiling loads is probably the biggest cause of this damage.
It appears that the missing pin in your frame is the joint check pin that was used to limit barrel travel in the older guns that used older cocking systems. It was rendered obsolete on later guns using the large cocking hook. Someone may have removed it because they didn't know how to remove the barrels from the frame. It should be replaced to prevent damage.Until then, be careful to open the gun gently, and don't permit the barrels to rotate too far. That could stress the solder joint of the forend hanger, which may already be compromised if the barrels were blued with hot salts
