It's not
too bad...
Drain the coolant.
Remove upper radiator hose.
Remove intake hose.
Unmount DCCV(may be easier to just remove it completely), aux pump and AC dryer.
Remove fan.
Remove the belt.
The book says you have to remove the oil filter adapter. I did since I wanted to replace it's seal, but you might be able to leave it in place. It's tight if you do.
Use a strap wrench to hold the damper still while loosening the damper bolt. If you turn that damper backwards (strap slips), you'll damage the timing chains and have to replace them and tensioners. I used an old belt for the strap.
Remove the damper bolt. Use a damper puller to remove the damper. Make sure not to lose the key (should stay with the shaft).
Remove the shaft seal.
Install a new shaft seal, using the custom 3.9 shaft seal install tool (otherwise very difficult to get it straight and at the right position.
Install the new damper (special install tool not needed). Use correct sealant on the key/keyway.
Install a new damper bolt, if you can find one. If you can't, then guess by feel at the correct torque to use for the old, already stretched bolt. Use the strap wrench again to hold the damper, but at least now if it slips it will be going forward and won't do any damage.
Re-install the belt (new one recommended).
Re-install everything else.
Fill and bleed cooling system exactly by the book.
Enjoy.
Official details:
2006 Lincoln LS Workshop Manual