IF you find that the Cusco springs are a 200mm free length (8") and have an ID of 62mm (2.5") then I can be of assistance to you. Go to
http://www.endura-tech.com and we have coilover replacement springs that are 6k, 8k and 9k in springs rates.
I think that you would find the 8k in front with a 6k in the rear to be ideal and all you would have to do is swap the rear to the front and buy the 6k (as you suggested in your post).
Best regards,