1968 340 Complete

You're right that it is an early 68 block. Keep in mind that they launch the next model year somewhere between June and July the year before. Your casting date is June 22, then give the engine plant time to machine the block and then assemble the whole engine. This would put the engine as being assembled as early as June 29th giving them a week to machine and build the engine. Just in time to launch the 68 models.