i think Leda makes a strut with the perch already taken off. might be an easy fit with the GC coilover sleeve.
I'm not 100% positive about it but check their website and find out.
THe Leda's are pricy though(something like $200 each), but have more ajustability then the Koni's.
There is a guy on this forum that had a custom coilover kit made by a Leda distributer but since it was custom i think he said it ran him about $2k
http://www.ledasuspension.co.uk/PDF%20Format%20sheets/Ford%20Mondeo%20Cougar%20Contour.pdf
