How to install a new ignition switch?

[Rui Roda]

Dear all,
First of all, as this is my first post, I would like to send a brotherly greeting to everybody in this Forum.
In my Model A 29 (RHD, that I bought when I lived in Argentina), the old ignition switch had a lock nut to fix it to the instrument panel. Recently I bought a new one (Mac's; see picture of both).
I have no idea how to install the new one in the panel (see picture).
What have I missed?
Thanks