Hello Mike,
Unique and Superformance use a flange mount on their header to sidepipe connection.
Go To :
http://www.uniquecobrareplicas.com/ and look at their fabrication shop and you will see a set of their headers. The SPF site does not really show their headers but check it out the next time you see one of their cars.
I have a Unique with a 427 in it and a SPF with a 460 . I like the flange connection vs what I have seen on other cars with a slip fit. The flange seals better and prevents the exhaust leak that gives you a backfire on deceleration. Seeing the grade 8 bolts all around the flange and the ability to put a cooper sealing material between the surfaces makes sure you have a good seal.
Besr Regards,
Tony R.