It really depends on use, but personally I wouldn't put anything smaller than 1.06" torsion bars in it. The key to running torsion bars of that size is the proper shocks though.
I run 1.12" torsion bars in both my Challenger and my Duster. Obviously, the Duster has a higher wheel rate. The e body 1.12" bars have a rate of 270 lb/in, while the Duster's 1.12" bars have a 300 lb/in rate. But the Duster immediately got Bilstein RCD shocks, and I haven't swapped the Challenger over from its KYB's yet. Even though the Duster has a higher rate AND is a lighter car to begin with, the ride is great. Very much similar to my g/f's 2013 Mustang with factory "premium" suspension. Definitely not like a typical musclecar, the feel is pretty modern and sporty. The Challenger is still a bit jarring, even though it has a lower rate and carries more weight. The key is having the shocks matched to the spring rates.
Both the Challenger and Duster are small block cars. So, with a 440, even if you don't want the same kind of handling I'm looking for I would still suggest something in the 1.06" range, paired with a good set of Bilsteins, Fox's, or QA1's.