Lowering a 67 dart

RAMCHARGED said

In other words new torsion bars in a higher rate & well matched rear leafs would give the same effects as adding sway bars to a car with poor spring rates(ie:sagging springs)But if you add the bars with well matched springs & T-bars you'll have a corner carver.

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Actually, sway bars (if installed correctly) theoretically have no effect on ride quality. They only come into play when one side of the car is more heavily loaded than the other. This most frequently occurs during cornering (obviously; this is the purpose of the "antisway" bar). When proceeding in a straight line, suspension travel, spring rate and jounce characteristics are unchanged.

In the real world, where you might hit a pothole with one wheel and not the other, you might occasionally get the impression that the suspension is stiffer or more harsh. But to imply that replacing worn springs would be equivalent to adding sway bars, or vice versa, is not correct. The two affect different aspects of ride and handling.

To summarize, higher spring rates affect the ride all the time (compliance over bumps, and body "lean" when cornering), but sway bars only affect the latter. So I suggest setting the spring rates where you are comfortable, then tuning with sway bars to achieve "modern" cornering performance (rather than 60s-style body roll).