You are correct in that a D would be for 1968, but that has nothing to do with the casting. I'm guessing you misstated. A "D440" would tell you the motor was used in a 1968 model car, but not what the casting date of the block is. There were lots of Hemi's cast in 66, and they were used till late 68 or early 69. The 3 17 (I think it was) is the asse\mbly date of the motor, which would be March 17.
Anything else stamped on there?
