I thought, as far as smog laws are concerned, if you bring a car from out of state, it has to meet the federal emmisions requirements. I'm not sure if you do have to convert it, though it probably has to have some emissions controls.
I would contact the local DMV in california, or find out information from the smog referee from the DMV. The referee's job is to either exempt or pass cars that fail smog, which will cost more than a certain amount to repair based on the years. so if you have a 1978 and the repairs to the smog would cost $300 and the max you would have to spend to be qualified for the ref, was $150 then you could get it refereed. the refs will probably easily be able to tell you what needs to be done for the smog if anything, or the DMV website for california is http://www.dmv.ca.gov.
You should be able to get information there, and possibly forms to fill out and all.
I had to get my truck refereed years ago when I had it, because it wouldn't pass and I had already spent more than the maximum needed. When I went to the referee station, they adjusted the car, and it not only passed the smog test they ran, but it ran better, and only cost me the standard fees for a smog certificate.
Hope that helps some