340 engine block w/no serial numbers

Are you trying to figure out if it's the original engine?

Look near the bellhousing flange for any stamping, top side are edge.

Being a 68 built that early, i doubt it has a VIN stamped anywhere.

The casting date on the side will be almost a dead give away whether it's the original. You're in a VERY tight window of casting dates being one of the first two months of 340 car production.