If you set the same ride height it should be fine. But if you're changing out the torsion bars for a different size you can't just count rotations on the torsion bar adjusters to reset the height, since the adjustment will be different with larger (or smaller) bars.
If you take some good reference measurements for the ride height before you swap the bars and make sure you put the car back where you started as far as the ride height is concerned the alignment should be the same. Even a small change in height shouldn't be critical unless your alignment is already on the verge of being out of spec. The most important thing to have right from a tire wearing perspective is the toe, which is pretty easy to check.
