[MidnightExpress]

Look for the build date on the flat pad in front of the driver's side bank of pistons. Your March block is probably a bit too close, while the Dec block is probably more in line. In another thread about the score of the day, there's an intake with a C8 part number and a 7E29 cast date. At the earliest 68 production, that would still be a 2 1/2 month span between casting and production build. I would go with the Dec block. But again, check the engine assembly date on that pad for both blocks.

This is the location of the assembly stamp the qouted member is referring to. It's the date when the castings after machining were assembled into a complete engine.