Looks like SB are different styles than BB?
Nope. All engines used the same size drain plug (1/2"-20 thread), but there WERE two different sizes for the hex head used. Up until sometime in 1968 (exact date unknown), the head used a 7/8" wrench, and then after that they used a 9/16" wrench. All were interchangeable other than that.
However, in answer to the OP's original question, even though the books say the changeover date was sometime in 1968, I've never seen a 68 Camaro with the early 7/8" head plug. Another interesting research topic?
Ed