Wagon rear springs are taller than sedan springs, and about the correct rate for rally use (a bit stiffer than ideal)
Assuming that you are still doing Marathon Rallies, the extra stiffness could be a blessing, considering the extra spares carried.
Early vs late springs are interchangeable, possibly with a change to the upper rear spring seats. I can’t remember the details because it has been a long time since I have thought about it, and because my brain keeps latching onto the early 140 vs late 140 rear spring differences.
I would definitely suggest converting the fronts to coilovers if the class rules allow it.