Howdy Jammer:
Most likely it is a C6DE, which makes it a 1966 casting used in the 1966 & 67 model year. "C" indicates the decade, "6" indicates the year in the decade. This is a seven main bearing block. The rods are of forged steel. The casting code is usually followed by a generic block code and a suffix, indicating changes from the initial casting. We have yet to figure out what each change may have been. Someone else may know.
Adios, David
