I unwrapped my headers today and found that the flange that mounts to the head is not flat like the stock manifold, instead it has a raised ring around each cylinder port. Do I have the wrong part or are the aftermarket headers just different? I have not tried to fit them yet, wanted to get an opinion first. They are the hooker long tubes, ordered from summit. Application was for 4.8, 5.3 and 6.0. I have the 6.0.

 

That's where the flange was welded to the tube. You can run the thick header gaskets and that helps it seal through them or get it ground flat and use the MLS factory gaskets.

 

my hooker LT's are that way..found out the cheap fel pro gaskets from local part stores seal better than the factory style, there thicker