Well, it was sold again, this time to a friend about 10 miles down the road from me. Not as cheap as it was the first time, but still at what I feel was very reasonable price.
http://www.ebay.com/itm/Rare-Repro-GM-19...=p2047675.l2557
It just got delivered yesterday and it looks like it's 1967 all over again. He claims it was the first design Chevrolet USA1 promo plate released before the ones with the painted letters and number. All I can say for sure is that I had the twin to it on the back of my 57 Chevy drag car back in 67 or 68.