that is very comfortable with physics.
If the engine were ejected upon impact with the tree, its momentum would have been in the direction of travel of the vehicle. Thus, the engine would have ended up in front of the crash site rather than behind it.
How do I know that it didn't roll backwards some 200+ feet after making contact with the ground? First of all, I seriously doubt that the engine, upon detachment, would spin rapidly like a billiard ball with low English imparted on it. Second, how long does it take for the rpm's of an engine to drop once the fuel supply and ignition system stop working? In other words, when you turn off your car, does the engine continue to turn over for some time, or does it stop immediately? In order for the engine to roll backwards, (poorly balanced) internal parts of the engine would have to continue to spin after fuel and electrical supply ceased. This is highly unlikely to the point of virtual impossibility. Third, even if the engine somehow had this very improbable amount of spin, it would have to overcome the great deal of forward momentum imparted to it from it traveling forward at the velocity of the vehicle.
So, my answer is no. The engine could not have rolled backwards some 200 feet. The JFK Magic Bullet Theory is more believable.
The engine was ejected at some point before the car impacted the tree and at some point before where the engine came to rest.