We don't have a lot of data, but so far it still points to 68 BB's being the velocity stack style and SS350's changing to the finned style about the first of the year.
More data will help, especially from both plants.
Specifically looking for data from SS cars with original hood ornaments:
- early (pre-January) SS396 cars
- mid year (~Nov thru March) SS350 cars
The condition of the car / hood doesn't matter, just as long as the hood ornaments are original.