I just did this job on a 600, they use the same bushings. There were many bushings, but it was the 2 on the top that made the horn go off by making contact with the back of the clock spring.
One was on the front, and other you had to push the shaft down and it was on the back side. There were clips that held it down in place. We did not have to unbolt the steering column at the firewall to do these 2 at the top.
If I am reading my notes correctly, I believe the part # was 111-997-12-40