Here is a website that lists restrictions for large motorhomes and tractor trailers.
http://www.dot.ca.gov/hq/traffops/trucks/bus-mh/busmap-d01.pdf
I believe that part of this route is restricted for Motorhomes 40ft and over and for tractor trailers with kingpin to rear axle distance longer than 30ft.
We have some great scenic drives in the USA but its no fun if you have a bunch of vehicles behind you and you don't have time to enjoy the view because you are looking for pullouts to let them pass. Its not about the roads driven, its about enjoying the view.
We can't drive the going-to-the-sun hwy because of our size. The best decision we ever made was to take one of the park mini buses on that route. Got to see sooo much more and it was an enjoyable and relaxing trip.
Never driven the California Hwy1 route, but now I am very interested. There are sections which I would drive in the motorhome...other parts I would take a car or maybe a maxi scooter if the weather is nice. Putting this one on my bucket list.
http://travel.nationalgeographic.com/travel/road-trips/california-pacific-coast-road-trip/