So there's a c6, a c7, and a c8 variant.
If the intake you have is a c8 and has an "S" cast on it then it is the "right" intake, it's just off by one model year. They're all about the same visually and were used on almost all the 390/410/428 4v cars from 66-68 except 428cj and 427.
If you're that concerned, then you also need to find the right date code - it should be anything from a few weeks to a few months PRIOR to the build date of the car.
