The internals of the Californian vs the Customs are identical on the GW II - you should observe no difference. I have a nickel GW II in .357 and I love it. I think the Uberti's are a good product, but I find them oversprung and a touch rough. THE GW II's are better this way.
I think $499 for a standard Uberti six shooter imported by EMF or Cimarron is a touch high, but its not outrageous. It probably is right around MSRP. For $499 you should be getting a steel grip frame and a case hardened or faux case hardened finish. Not a matte finish, and not a brass grip frame, which are the unauthentic touches found on Colt clones (among others).
The GW II Customs have a genuine color case hardened finish by Doug Turnbull. The Californians have a case hardened finish which is no doubt better than the Uberti's, but I don't know if it's 'genuine' or not. It looks pretty well done. I am thinking of buying one of these Californians myself, and would be very interested to hear what these finishes consist of and how they hold up.