I doubt it's a 66-67. Which are very high grade. I don't see the whole coin 63 is possible. Not really worth much. A 1960 small date Philly in MS 65 would be very nice. My over priced high retail online guide has it at 20 cents in MS and 30 cents in MS 65. Which means even if it is worth a dime, there's no market for it. Are you going to pay to have it graded?
I see the coin in the other thread. I think 60-63 is likely. While it may be a keeper, the value is very low.
For a true sm/lg date DDO for this year, the zero is the more telling as in this small over large date. You can see the smaller zero (red line) centered over the large zero ( blue line). It is also a D/D Wide RPM.
No, 1968 marked the beginning of S proofs (a really basic piece of knowledge EVERYONE should know). Prior to the 1965-1967 hiatus, all proofs were plain, without mintmark, and struck in Philly. I was once struck in Philly, but that's another story for another occasion.