Ontario allows car owners to put vintage plates on their car provided the car is at least 30 years old, the plates are the same year as the vehicle was manufactured and as long as the numbers on the plate are not in use on any other license.
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I checked with the Ontario Ministry of Transportation and they confirm that this number is available as Year of Manufacture plates for your heritage vehicle. To verify - show contact info
If you've got a 1968 car then these plates with number "100-73X" meet all the criteria. The plates are blue lettering on white.
The one plate is in excellent condition with virtually no rust and just a few minor scratches. The other is in similar condition except for a crease across it.