Do I need to remove the header to replace this gasket?

You'll need to unbolt the header from the cylinder head — the gasket sits between those two surfaces. Full removal isn't always necessary, but you'll have better access and a cleaner seal if you do pull it completely.

Will this gasket work with my current header, or do I need a new one?

This gasket works with any header designed for your platform. If your current header is warped or cracked, no gasket will seal it properly — inspect the flange surface first.

Do I need to prep or clean the flange surfaces before installing?

Absolutely. Scrape off all old gasket material and carbon buildup from both the header and cylinder head flanges. A clean, flat surface is what makes this seal work — don't skip this step.