I just installed a Nardi wheel on my 230SL with a hub #3319. The wheel is about an inch higher than the normal wheel and I was able to make the horn work with a little work (insulated the ground pin on the horn contact ring). The #3320 hub will not work with the horn connectors and it is at least another inch taller than the #3319.
Jim Villers
190SL, 230SL 5-Speed, 190E 2.3-16 Kompressor