Location of Vin number on 68 340 block

If a block has a cast date during 1968, it's more likely to be a 69 model year than a 68 model year. Maybe the first 4 months of the year could be 1968 model year engines. Most stuff after April was likely destined for a 1969 car.

If it's got stampings from the factory on the rail pad it's 69+ model year engine.