Sometimes high performance headers aren't always that easy to seal. We at LRS have dealt with this many time and came up with this Extreme Exhaust Gasket kit for 1993-1995 Lightings running a 5.8L based motor.
These kits Include a set of our premium Copper header gaskets and a set of (16) locking header bolts. The Copper header gaskets are designed for high performance applications and the Header fasteners absolutely, positively will not back out. Using these locking fasteners Eliminates the need to monitor and tighten bolts regularly. They are made of Grade 8 aircraft quality bolts that are made right here in the U.S.A.!
I have been ordering items from Latemodel Restoration for many years. I've found them to be exceptionally professional, timely with order processing and shipping correct items ordered. I've never received an incorrect item on an order.