Only illegal if it was intentionally titled as a 67. If it was a clerical error, just chalk it up to human error. Did the seller explain the back story as to why it is titled as a 67 or did they just say it was titled as a 67 and leave it at that?
For instance, when I had the form filled out for a VIN verification on my Valiant by a police officer, my car was accidentally titled as a hardtop, when it is actually a sedan. No deception was intended, just a mistake.
We need the back story before we crucify the seller.