Which torsion bar to use?

72Valiant4Door, I am not sure if I agree. If the spring rate is too high, the tire won't stay in contact with the road over irregularities as well as it would with a lower spring rate (it will display the "baby buggy" or "roller skate" effect). The Porsche is an example of a good-handling car with a relatively low spring rate. I think you want the maximum spring rate that will still allow the suspension to float a bit over bumps.

Do some more research on Mopars that handle. You'll see that most use large t bars. The Valiant I own is regarded as the most track capable stock type suspension A body in existence and it has 1.24" t bars.