https://www.classicparts.com/1947-53-Ignition-Switch-Original-Style/productinfo/53%2D405/

https://www.classicparts.com/1947-53-Ignition-Switch-Bracket/productinfo/53%2D461/

The bracket attaches to the rear of the dash.
As I dimly reall, the switch is twisted to catch the two posts.

I do not recall if there is an attachment nut/scew(s) for the switch to the bracket.