We've all sold cars we didn't really want to sell, and there are certainly cars I regret selling. That's life.
"When the car comes home?" Unless you have some contract documentation between your dad and the guy he sold it to, then all you have is anecdotal evidence that won't stand up in court.
Let's face it, if you had evidence that the car was actually stolen, you would have it back by now, just like this guy has his E-Type back, which was actually stolen ...
Stolen E-Type Jaguar to be returned to owner - 46 years on - BBC News