DanileG to answer your question yes they are Antique plates and yes you use them to go show's and as luck would have it I took a first place (I will post a picture of the trophy/plaque soon) at the 55th AACA Show (longest running and oldest car show in America i am told) in Lake Forest Il.
I have not been stopped yet...for not displaying front plate. But I know someday I will. (did I mention I took first place?)
A friend of mine told me that in Illinois there is a law that say's you can display a plate that is from your model year. For instance my buddy run's a 1934 Illinois license plate that he found in good condition at a swap meet on his Bonnie and Clyde 34 Ford. He did say that he often get's pulled over by Barney Fife and has to show the AV plate's along with the paper work that he got from the IDOT folks that states that you can run Illinois plates of your model year as long as...You have legal AV plates registered and have the slip of paper that states you can run said plates...and you are on the way to a show or running to or from a mechanic. I happen to have a mechanic friend in almost every town that I drive in and keep their phone numbers with me ...if you catch my drift.
This same pal of mine just found a nice set of 1972 Illinois plates for 25 dollars that I will buy for my 350 SL. I am in Lake Bluff Dan where are you? :p

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I love low mileage cars!
1972 350SL 23,000 miles
.......Sold...........
Now 1969 280SL