You won't have a problem if it's a US-spec car. In fact I'll bet your 600 is 50-state certified since there weren't that many of them made/sold. If it's a Euro-spec car, there's a special one time inspection in store for you if it was not federalized specifically to CA code.

Not a problem if you're coming in from Canada with a Canadian-spec car either.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD