I am been searching for a a license plate Ohio 1970 that has JK and the number or J number K I have been looking ever since I acquired my car over 2 years ago I have a EBay search and I know that they made such a plate southern Ohio area and it exists maybe in your travels you might run across such a plate will reward you handsomely for your find!
Have one made using pieces of various plates to make the letter number combination you desire.
That's how they do it here. ::)