If you are going to swap in coilovers you are also looking at redesigning the whole suspension. You will have to run a 4 link, 3 link, torsion bar, or some other different suspension to run coilovers.
There is probably some info in the Center of Gravity about this type of stuff. There is no easy way to swap in coilovers into a K5 as of right now. It will take alot of fabrication and math to get it right and installed.
Harley