Yep, Dave is right! Prior to 68, the casting date is the only way to date a block, except for the pad below the drivers side head in front, which will tell you the assembly date, the displacement, and the model year of the block in alphabetic code! If there is no alphabetic stamp and it's an LA motor, it is a 64 273, an "A" would indicate 1965, a "B" would be 66 and a "C" would be 67. After that, the vin started showing up on the bottom rail of the block on the passenger side, right above the oil pan rail!!