Thomas,
My understanding of torsion bar suspension is that it uses the twist resistance of a bar to do the work of a spring... ie, the inner end of the bar is attached to the vehicle, the outer attached to the hub assembly. As the hub assembly moves up and down, the bar resists the twist thus return the hub to its neutral position.
With respect to Guy, my '79 Subaru had torsion bar suspension, I thought it was actually quite common.
In theory, I would have thought it should be simple to "lift" a torsion system as you would only have to fit a bar with an offset securing mechanism at the inner end (ie, same as artifically pre-twisting the shaft). You may need to alter other components to keep the wheel central in the arch but if you are buying a kit, I'm sure this is all accounted for.
I have no doubt that the OME kit you are looking at is well designed and may use better material for the torsion bar that can provide more movement at the hub end etc.