[1crosscut]

My thought is that the slot is not a stop but indicates the limits of the full range of the spark advance lever.
Most likely if you have a two tooth steering column the column will need to be rotated for the correct range of motion. If it’s a 7 tooth you may need to bend the arm on the steering column that the linkage fits onto. A pair of pliers will bend it.
I’ve bent several of them and have not had one break on me.