1) Beefier TB's stiffen the ride, and
2) New spring will always be an improvement.
Given you have replaced all rubber parts, and ball joints in the front end, the beefier TB's will do this:
The front end wallows less, and when the front end hits bumps in the tarmac the car feels more stout. As if it had more muscle to wrestle the road. Makes the car feel incredibly strong. But the bigger TB's will also transmit more vibration to your steering wheel. Not much, but some. That was a major design problem with torsion bar suspensions from day one. So it's a give and take situation. Which one do you value more: the original floaty ride, or the ability be in more control of where the car is heading? - I did like my 1.06" FF TB's a lot. But that is just my .02 cents.
However, I would never put old springs into my car. Period. The spring metal creeps under stress. How much, depends on the load, temperature, number of pulsations (cycles), and time i.e. how long the spring has been under load. A fifty year old TB will have less than 80% of it's original spring rate left. No amount of turning the TB bolt will revive what is lost of the spring rate. You will get the front end higher, for a time, but that is all.
If you like the original ride, go with OEM spec bar.
BTW: Chrysler Corp. added the TB diameter in 0,02" increments, as it's the outer surface only that's needed to resist torsional force. In theory you could replace the TB's with hollow tubes of the same outside diameter.
FF TB's have two gaps here that'd need to be filled: they have a 1.00" bar (which is a good replacement for a 440 A/C car, which originally had 0.98" bars), but no 1.02" or 1.04". The 1.06" might just be too much to those who favor the OEM floaty ride.