383 engine identification ?

If it has a 1966 casting date, chances are better than not it is NOT a 68 motor. It will (probably) be either a 66 or a 67. It will probably have 516 heads (if they are original to the motor) and will NOT have a freeze plug in the end of the head. Assuming they are 516's and they have not been modified, they will have 2.08 and 1.60 valves in them, and have small intake runners. Bad thing for a high twisting 383.