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.