72 Dart Swinger Wheels

A sagging leaf spring or torsion bar could be the problem too.
A 205/14 radial will be close as you get to the bias ply tires that came on the car. Radial have wider and softer sidewalls though so it still wouldn't be perfect. My 67 rides much better on 215/75/14.
If you are bound to buy wheels double check the bolt pattern beforehand . May be 5 on 4 inch circle or 5 on 4.5 inch circle.
Good luck