What size torsion bars for a 383 in a 75 Dart?

Dana67Dart said
The bar diameter and length sets the spring rate. Lower spring rate can be set to the same ride height as higher spring rate (within some limits.) The main diferences with a stiffer bar will be harshness of the ride and cornering performance.

and?

a 1+ inch bar with a big block will be far from harsh. hell its not even harsh with a small block on the larger bars.