People that are concerned that a 1 inch torsion bar will be too stiff have never driven or been in a car that had them.
My 70 Charger has 1.15 bars and rides about as firm as our 2015 Challenger R/T. The torsion bars and leaf springs need to be complimented by the right shocks though. For many years, I had 1 inch T bars and KYB shocks. Now, The car actually rides better and has more control now with bigger T bars and Bilstein shocks.
A 383 or 440 A-body needs more spring rate than a 318-340 car. Mopar had soft spring rates back then. Bigger torsion bars are just a part of bringing the ride and handling quality up to modern standards.