That flange on the right exhaust manifold is OEM stock. I can show you pictures of two I've done in the past few years that are identical. It's the OBX headers that are not designed to mate with the stock exhaust. I did OBX headers on my car and had the exact same issue. You have to have an adapter piece fabricated for the headers to mate with the flange on the exhaust. Similar to what your seeing on the OEM manifold. Or... you can cut the flange off the exhaust and use commonly available exhaust pipe adapters to mate the headers to the exhaust. I've done it both ways.
H
