Just because you have the logbook doesn't mean you own the car. If you take a car that isn't yours you have stolen it. If you get the logbook in your name you've still stolen it. If you sell it and the owner comes looking for it, expect the car to be returned to its owner, and you to get arrested for theft.

Having said that, the police are useless, they'd probably advise the owner to pursue a private prosecution and nothing would come of it so you'd be alright. It is still illegal though.

Charlie