Japan Plates on my Z.

ShutokuZ

There are no states that will allow you to register those, as your own plates. Even if you could here in Cali, you would still need two matching, in which you said you only have one.
When I imported my e36m3 from Japan, I was running on Japanese plates for two months, waiting to get the registration translated. I got stopped and pulled over about once a week for the plates. Never got a ticket though, as it was legal to do, since I did have the paperwork from the DMV.