Part of why I said what I did is that if you take a look at PCGS Price Guide & Coinfacts, having a 1960 MS-66FS means maybe a $14k coin. In proof, it only becomes a high dollar coin in PF-69 DCAM, and even that tops out at about $6k. What I mean by all of that is to point out the odds.
Beyond the odds, I have specifically been in the market for early Jefferson proofs for a little while now and that's pretty much all I have looked at. I feel confident that the coin in question is a proof. Microanalyzing the exact shape of the rim may not be a good idea.
Compare the MS-66+ I posted (not mine, by the way) and see the differences in strike quality across the board. Also note the lack of
Die Deterioration effects on your coin. It just...has that
look of a proof. Even the haze on it from being in Mint cello looks like proof haze.
You could always submit it. I certainly don't want you to miss out on anything because you took my word for it. If that did grade something like MS-67FS, it would be a
very valuable coin. I can't offer advice on what to do, just my opinion on what it is.

In Memory of Crazyb0 12-26-1951 to 7-27-2020
In Memory of Tootallious 3-31-1964 to 4-15-2020
In Memory of T-BOP 10-12-1949 to 1-19-2024