towing 4 speed dart with Tow bar

I was always told that if you flat tow a car you don't want the differential spinning. It rides on the the coast side of the ring and pinion, and it will wear out quickly. Don't know if it's true or not, but it does make sense.
I would never tow a car 200 miles at 70 mph. Buy a trailer and be done with it. Plus you get 4 more sets of brakes on a tandem.