On older guns, chopper lump barrels were of quite mild steel. Since the lump is of the exact same material as the tubes (one forging) the hook and bites will be soft. I don't know of any way to case harden a spot such as the hook and they are of too low a carbon content to take heat treat. Dovetailed lumps could be case hardened prior to assembly if they were soft soldered. Since it seems to be common practice to braze the barrels and lump of a dovetaile assembly, any case would be annealed. all in, I doubt you will find a hard hook on an older gun. One would hope the pin was, in fact, harder than the hook unless the pin was threaded and intended to be replaced.
IMO, the hook/pin wear comes from cycling the gun open and closed. There should be very little movement between the hook and pin during firing. Has anyone heard of hook/pin wear data comparing open/close cycles with firing to cycles without firing? I agree with Chuck that you need to preserve the front lips of the hook inlet to maintain vertical alignment. However, if the pin is worn, you may change that alignment slightly with filing of the weld metal to set water table clearance. The gap between barrels and water table is necessary to give the action bar room to flex upward during firing. If the barrels are in contact with the water table, the action bar flex load is transfered to the hook/ pin, to the bolts/bites, and to the barrel breech and face. That load is sufficient to move all the mating surfaces relative to each other and that will quickly produce off-face.
