In california, if you can find two matching plates from '62 on back and have the same year car to match, you can bring them to the DMV and register them to your car. From '56 to '62 all cars used plates that said '56 and had a metal tab added to yearly registration. I had a '58 done up this way.

In '62 cali went to the black & gold plates. I think around '70 they went to blue and gold. You can keep the black & gold plates as long as they are on your car, but you can't put them on if it was ever registered with later plates.

You can keep the vanity plates, but they only became available in the blue plate era. The only exception to this is the dmv had amateur radio call letter plates in the black era, and you do see some of those on new cars.

At one time the cali dmv wanted to collect up all the original black & gold plates so they could release a special plate the USC folk. This didn't sit too well with the classic car folk.