Why headers? They raise the underhood temperature, leak, blow gaskets, and burn plug wires. Also, there's no measureable power advantage under 3,000 RPM, even with a stock camshaft. The only time I've seen a worthwhile power advantage from headers was on a tractor-pull engine with custom built equal-length tubes on a Dodge 440, and the primary tubes were 8 feet long, going into a 6" collector. Those headers allowed us to build in a measureable torque gain at 2,000 RPM, and the HP topped out at 714 at 6,500.
Jerry
