72 Dart Torsion bar replacements??

They aren't cheap, prices have gone up quite a bit since I bought mine a few years back but Sway-A-Way still sells a full line of bars ranging from 0.87" to 1.24" 1965-1976 “A” Body – Sway-A-Way

I had 1.00" bars in my Duster for about 7 years made by Just Suspension (company no longer exists) with an iron-headed 360 and the ride was no different than with the stock 318 bars but handling was much more sure-footed. I now run 1.14" bars with an aluminum-headed 360 and now the ride is more like a modern car but still not harsh, surely not helped by my soft stock-replacement shocks which make it feel more bumpy (yes that can happen, underdamped suspension will ride poorly). I've driven/ridden in stock modern non-performance import sedans (Camrys, Accords etc) that have a worse ride than my Duster did with 1.00" bars and not any better than now with big 1.14" ones.

@RustyRatRod I highly doubt 1.03" bars would be "too much" in a slant-6 A-body but if you're really after more of the old-school boat-like experience you could go with the 0.94" Firm Feel or 0.96" Sway-A-Way pieces. I personally would not run any diameter smaller than that for any reason aside from a purpose-built drag car. Cars with torsion bar front ends do not react the same way to higher spring rates like coil-spring cars do, it's not a linear trade-off between ride quality and roll stiffness. Admittedly though I'm a bit biased and find stock-sprung classic Mopars to be not very enjoyable to drive with how much they roll in turns and how much you need to slow down on curvy roads to not slide off stock-type seats, especially a bench.