I have a 930 but not the JM version (wasn't out when I bought mine).
Was having hell getting slugs to hit where I wanted.
Got the Hi-Viz Four-in-One sights with the tall front sight and it now shoots perfectly.
I just received the same sight and used one of the screws provided in plave of the original sight. Did you use the double face tape or did you drill and tap for the second screw?
What is the drill and tap size needed for the other screws they provided?