Why cant I crank up torsion bars if front air susp. down?

[pcweber]

OK, so I replaced the rears with the coils and rear is up fine. I read a post where if you replace the shocks with the Bronco shocks instead of adjusting the torsion bars you don’t have to get alignment or install the caster/camber bushings. The final intended result is to have the control arm pressed down farther by something, whether it be the torsion bar or the shock with an overload spring on it or the original air shock with air pushing down on it. Can someone explain why there is a difference that would change caster/ camber if this effect is accomplished from the torsion bar and how it does not when applied from the shock absorber?