Rick, there are SMS coins for 64 http://www.pcgs.com/News/1964-Special-Mint-Set-Coins I can tell, though, if these are SMS or just proofs. I'm leaning toward proofs because the rims on these look like proofs.
Also from the PCGS link above, I believe these are proofs "The surfaces are non-reflective compared to proof coins of the era" I see mirrored fields in the OP's coins
I think the only SMS 64's that ended up out in the wild all came through the former mint directors estate. I mean it's possible that some ended up being distributed in the normal distribution of coinage but I'd think the probability of them being in a proof set wouldn't be as great as that of being in a regular mint set. I mean since the SMS coins clearly aren't proofs I doubt the mint would have used them to mint coins then distributed in proof sets. Although since the SMS coins closely resemble business strikes; I could see the mint having reused the dies they struck the known 64 SMS sets with to continue striking business strike coinage. In a way similar to the reusing of proof quarter dies on business strike coinage that resulted in type B reverses, etc. It's just a theory on my end though no concrete evidence.
1964 Kennedy SMS known number is 12-15 . One of our members owns the finest one graded by any Tpg but Pcgs