Will these headers bolt straight to my factory manifold studs?

Yes. These mount at the original bolt points—no drilling, welding, or additional brackets needed. You'll need your existing gaskets and studs; bring fresh ones if your originals are worn.

Do I need to prep or paint the headers before installation?

Stainless steel doesn't require primer or paint. Install them as-is. They'll develop a heat patina over time, which is normal and doesn't affect function or durability.

What size are the outlet flanges?

Mounting method and outlet spec aren't detailed in the listing. Test-fit your existing exhaust system before finalizing install; you may need a mid-pipe adapter depending on your downstream setup.