In 1967 all cars were supposed to be marked with the partial VIN. Before that only HD or high performance parts such as your 396 and the TH400 where marked with a partial VIN. So both the engine and the tranny should be hand stamped with the last six digits of your car's VIN on ther motor ID pad and on the side of the case just above the oil pan on the tranny.
The 12 bolt rear end may or may not have been marked as well on the differential case somewhere around the fill plug. The axle tube on the passenger side front middle of the tube is marked with date of the build, plant ID, and a code for the gear ratio. If it was a factory posi that info was also marked on the tube in the same place.