Steering Wheel Swap....any advice???

Changing from stock wheel to a Grant Classic on a '74 Duster. My horn button is round compared to the horn button that is shown in the Haynes Manual.

1) How does the horn button come off?
2) Do you have to remove the turn signal cam to install the installation kit and new horn button?
3) Any other little hints I can get will be appreciated.

Thanks,,,,,,,,,,,,,,,,,