Chrysler didn’t start stamping partial VIN’s onto the blocks until sometime in 1968. Depending on the plant, it could have been early in ‘68 or mid ‘68. Therefore, anything before ‘68 can only be ‘date code‘ correct for the car. The engine would have to have a cast date prior to the build date of the car, anywhere from a month to several months before. Anyone who tries to sell a pre ‘68 Mopar as numbers matching is trying to pull a fast one; no such thing exists.