Do I need to clean or prep the header and cylinder head surfaces before installing this gasket?

Yes. Scrape away old gasket material and carbon with a gasket scraper or brass brush until both surfaces are clean and flat. Wipe with a clean rag—no oil or debris. A clean seat makes the seal work.

What torque spec should I use when bolting the header back on?

Refer to your vehicle's service manual for the correct torque sequence and spec. Uneven or over-tightening can crush the gasket or crack the header flange. Tighten in a star pattern in two passes.

Can I reuse my old header, or does it need to be replaced too?

The header itself rarely fails—it's the gasket that wears out. Inspect the header flange for cracks, warping, or deep pitting. If the sealing surface is flat and undamaged, reuse it. If cracked or severely corroded, source a replacement header.