I Just installed Headers on my '97 Mark VIII.
Here's the deal, buy 1 5/8 x 2.5 DOHC Headers for '93-95 Mark VIII FROM SUPER COUPE PERFORMANCE. You will also need long lead O2 sensor, 4.6 DOHC Header installation kit, and I opted for the Tru X Box..Call Bill at Super Coupe (513-697-6501) he will explain why it might be best to install the '93-95 Headers and he will not sell you anything you do not need.
I installed the Headers without any modifications to the original steering system..NO PAIN, NO STRAIN.
Tip: When I installed 2.5 Mandrel dual exhaust, I found $6.00 bent 2.5" exhaust pieces at NAPA that connected headers to the exhaust system/X Box.
I sent pictures of the installation to John Peters (LOD), I think he will post some of them in the Members Ride section soon.
If you live in the Virginia Beach, Virginia area and want headers installed on your Mark VIII, give me a call, Charlie 757-620-7733