This site shows a similar plate in 57 -
https://ncplates.weebly.com/chevrolet-plates.html
but says they were all colored backgrounds with white letters, and the font is a little different too. If you open the pic from this site in a separate window and enlarge it, the holes are oval like the 60's USA-1 plates, not the rectangular holes present on the eBay plate. So I would guess the eBay plate would be older than 1957? Or maybe an unlicensed knock-off of the 57 plate made by some other vendor back then?