There are at leas three ways to make a hook on a lock plate.
# 1 and the easiest way is to solder it on with fine silver. Fine silver solders well and melts at 1760°1f so the lock can be case hardened afterwards without the hook coming off.
# 2 is to chisel a slot in the plate and stake the hook in the slot much in the same way a barrel hoop is put in but with an elongated slot.
#3 is illustrated in the drawing below. Sometimes the hook was wide and just hooked into the wood and sometimes a lip was made on the lock plate that just hooked in the wood in the front.
There were only two logical reasons for a hook to be put on a lock plate That I can think of. #1 is so that any side plate could be used even if it did not match the holes in the lock plate. #2 is to avoid the ramrod channel with the front lock bolt . In any case it was quite common on English Firearms in the 18the century.
PS-- sometimes a small plate was placed down alongside of the barrel channel and the hook screw in the stock was threaded into the plate