Matching Engine to Production Date - Pre-'68

Hello All,
I am aware that before 1968 these cars did not have a partial VIN stamped on the block to determine with certainty that the motor and car matched. However, let us say that a person was looking at a pre-68 Barracuda that had a production date on the tag as April, and the date embossed on the engine was 8*14*67, which is of course after April. What are the odds that this engine originally shipped in the car?
Zero.
Closest you would come to that being original is if the engine got blown up early in it's life and was replaced with a warranty engine.
You can't have a car assembled in April with an engine that wasn't even cast (or assembled-depends on the number you're referring to) until August...