I don't have the answer. My Hollanders show the mid 60s as having plastic centers and these appear to have solid centers.
these hub caps have removeable centers that are plastic. they are held in by a triangle clip on the back.
Look on ebay,swapmeets, hubcaps are cheap. If you can get $50 for the set you will be doing good. Especially 14 inch, not many people running them it seems.