Just ordered new cat assembly's for both sides of my 2004 fx4 I have new bosch sensors coming for them also. I am looking here..http://www.villagefordparts.com/auto...-manifold-scat

and cannot see any exhaust donuts or gaskets for the attachment coming from the Exhaust manifold to the cat assembly is that correct? The reason why I am putting new cats on is I am getting the code changed sensors and still there it has 234 grand on it.

 

They are a Conical Ball type seal.
The pipe has a rounded ring, the manifold has the socket it fits in.
A two or three hole clamp goes on the manifold studs to hold the seal together.
Good luck.

 

What kind of cats did you replace them with? I am looking at doing mine. Probably just the front 2 and delete the rears.