Whoever had the original car stolen from them needs to go claim this one. I've seen where cars stolen 20 years ago were found and returned to the original owner. He may have to pay back the insurance. I wonder if the stolen 68 tag is covering the VIN of a stolen 67?
Depending on state laws, prosecution of the persons who stole the vehicle may be barred after so many years. However, the lawful owner of the vehicle still owns the alleged stolen vehicle.
Whether the person that currently holds title is the thief or not, does not own the vehicle regardless of how much time has passed.
Possibly at the time of theft the owner had no insurance or possibly the insurance paid it off. So either it goes back to the original owner or the insurance company.
What the person who knows about this vehicle should do , if you know where the vehicle is and have proofs that at one point it was reported missing or stolen, is to contact the police where the vehicle is and ask the police to recover or look into this situation.