Look at the pic.
Spring on the left... is a rear spring. Very little taper from top to bottom.
The shock assembly on the right... is a front spring. You can see the noticeable taper of the spring, from top to bottom.
You can now see the components of the shock assembly. Top plate, spring, bottom spring isolator, and shock body. That complete assembly is held together by the big nut on the top plate... and bolts into the shock tower... and attaches to the lower control arm.
Jaguar made all the springs the same size on the S-Type. Bilstein made the shocks to fit the Jag springs.
The Bilstein shocks will fit the spring on the left... but obviously not the one on the right. Ford did a different design on the front of the LS, for whatever reason.
The problem is... that the lower spring isolator (white disc at the bottom of the LS shock on the right)... will NOT fit on the Bilstein shock.
The "work around" for that... is to get 2 used LS rear shocks from a junkyard... and carefully remove the lower isolators (white discs) from the boneyard shocks... to install on the new front Bilstein shocks.
All this... is in the suspension thread I created.
Warning... if you do this... I suggest you take all the parts to a shop... show them this thread... and have them assemble everything for you.
ESPECIALLY if you have never used a spring compressor. One wrong move... or if the spring compressor breaks... the force/pressure of the spring could severely injure, or KILL YOU.