Towing With an Undersized Vehicle
I don't know whether your Dart's owners' manual included the design parameters for the weight distributing hitch platform, but the attached file has the basic parameters. Since factory built trailer hitches weren't as common in the '60s as they are now, Chrysler included the diagrams so that you could have a qualified welder construct an appropriate receiver hitch.
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)