Ok, I screwed up and ordered a new genuine volvo head pipe and a Bosal cat listed for a non-EGR car, but figured out later that my 1992 240 wagon IS an EGR car. I can;t figure out what could possiblly be different if both head pipe and cat are being replaced at the same time.

I know that the head pipe to exhaust manifold is the same, and the 3 bolt head pipe flange to cat 3 bolt flange should match up? What am I missing? Oh, the existing exhaust has the 02 sensor in the cat, but it is a hillbilly rigged universal POS cat. Some idiot PO hacked off the 3 bolt flange and rigged up an aftermarket cat It's a california car, rusted and busted in the Ohio salt. Thanks!