On 68's vin is on dash, paperwork, and likely on original engine and trans top center where engine mates to trans.. Some early cars did not have eng/trans stamped.
The so number is on the fender tag, rad core support and trunk rail, and paperwork except title.
If you have a title and a dash that matches, that's all he'll have. Then it's look closely at the dash vin plate and rivets.