I'm replacing the rusted out exhaust manifolds on my 97 4.6 with a set of Summit/Pacesetter shorty headers, and the flanges on the headers don't line up with the ones on the top of my cat pipes. Am I correct in assuming the flange is a slip fit behind the flared end of the cat pipe, and that I should be able rotate them a little to line them up with the headers if I can break the rust-bond?

 

They shouldn't exactly slip fit but connect on both ends and maybe a 1/2" of pipe will slip into the down pipes. But if they dont match up, it would be a tough call without seeing.

 

I don't have a picture of my truck handy at the moment, but the connection is a ball flange, similar to this: http://image.carcraft.com/f/9219702/...all_flange.jpg

I'm thinking that the flange ring on the pipe should be able to move so its bolt-holes will line up with the ones on the header. They're pretty solidly stuck in place right now and I was trying to verify that my theory is correct, hopefully with someone who's already been down this road, before I try to break them free.