FYI oscar,
Coilovers are dampers/struts that hold the coil at the bottom by an adjustable platform, so you can raise and lower each corner of the car as desired. A normal damper/strut has a fixed bottom platform and the ride height is varied by changing springs.
The clamps you are refering to squash the spring to remove the pre-load to allow the top nut (that retains the top of the spring) to be removed.
I've recently fitted Eibach springs and dampers on my car and yes I'd agree the front does sit higher than the back, just as it did as standard but just a bit lower. Might have to give the front springs a wee cut

I think the springs alone would be OK providing your dampers are in good condition, its perhaps not ideal for real performance driving but you'll get away with it.
Hope this helps