It is an S series, I do know that, and the first three serial numbers are 257 which probably makes it a first or second year gun. The Smith book says the model started at 256500 so in best case it could be one of the first 500, number 257000 or in worse case, number 257999 making it one of the first 1500 guns made.....if you trust the big book of Smith. So I would guess it is a 64’ or 65’ Model year. I am liking this deal more and more, thanks to you guys.