Yeah, run the saxo up and pull the immobilser box off right? I'm hoping to sell the back axle and get a cheap drum beam as the arches aren't that big on a 4 door.
Yeah, that's it. Unplug immobilizer box whilst its running. Hang on to it and test that it starts again a few times before taking it all to bits. Perhaps leave it half an hour just in case.
The disk beam itself is the same as a drum beam - the radius arms are the same, torsion bars interchangeable etc, but the AX beam might not have an ARB. The disk setup ends up about 3 or 4mm a side wider, nothing too much.
As far as I'm aware the 3 and 4 stud drums are interchangeable if you swap the backplates too.
For example mate is running a base model 2004 saxo beam, with s1 106 XSi torsion bars and ARB, with VTS stub axles and calipers.