[First opel 1981]

Does your state provide for abandoned vehicles?
In Oregon, if you have a vehicle on your property for more than 30 days you can file as if it is an abandoned vehicle. There are forms specifically for this. The state then sends a notice to the last registered owner and gives them the option of doing something about the car. If the registered owner does nothing then after an additional 30 days you can file for title to the vehicle.

This lets the state do the legwork.

Alternately, you could sign the dead guys signature transferring title.....just kidding folks. That would be illegal. Seriously, don't do it.