I decided I wanted to use plates that would have been used in 1973 on my '73. Each time I called DMV I got a different answer. I was first told that I had to find a matching pair of retired plates. The first interpretation was that the actual numbers on the plate had to be retired, not just the plate style. This proved to be an impossible task, as the number sequences get recycled routinely. Another call to the state DMV yielded a different interpretation. I finally had a state worker read the policy to me over the phone. It became clear that the policy simply states that the plate style must be retired and that you must run an original matching pair (no reproductions) from the YOM. I was able to buy an excellent pair of appropriate plates in an antique store for $6.00. I was still required to register my car as an antique, buy the designated plates, and keep them in the car with the registration paperwork.
The California situation seems to show different interpretations as well. I'm sure there is a definitive answer, but it isn't helpful to have as many interpretations as there are state employees attempting to provide an answer - which can sometimes work in your favor (wink).