So
Wheel Rate = Spring Rate * (Motion Ratio^2)
The HDK has a motion rate of .807, so yeah a 450 lb/in spring yields a 293 lb/in wheel rate.
If you wanted a wheel rate more like 120 lb/in and you had the same ratio you’d need a 184 lb/in spring.
If your motion rate is .77 then your 120 lb wheel rate would mean a 203 lb/in spring.
As far as seeming soft, a 300 lb/in torsion bar is 2.5x stiffer than a factory .87 bar (120 lb/in), so it’s a pretty similar change.