I don't know about it being in the same class as a split window Vette...but I understand what you're saying. You may have the oldest, definitely the oldest documented to date. Also, 165 would put you into 1965. I personally theorize that the first number in our case was the year of production, not a literal sequential number while the company was still C&S.
I'll have to look through my pics and see what I can dig up for the sole. My original casting deck is behind the barn, so I can get new pics from that if need be.