So it doesn't take much to work out my plan for these.... $40 each from breakers. These are from a 2001 Subaru Outback Limited.
As you can see the rails are asymetric; flat(ish) mounting on what would be the 'outside' of the car, but vertical on the 'inside'. I figured that it would be easy to switch one rail over... but no!! The driver seat had a height adjustment which meant the rail was welded to a bracket, after some 'application' of an angle grinder it was removed (and I also had to cut off the seat belt bracket as it interfered with the adjustment handles).
Some slight changes were needed with rail adjustments, but now the seats are symetrical and sit nicely. My test drivers approve
Next is to measure up the mounts and figure out the design for the frames,
Simon