Do these headers need any painting or prep before installation?

Stainless steel won't rust and doesn't require paint. You can install straight out of the box. If you want a polished or coated finish, that's cosmetic and fully optional.

Will these fit my original manifold bolt holes?

Yes — these use factory mounting points. No drilling, no new holes needed. Bolt directly where the original manifolds attached.

What gaskets or seals come with this?

The header assembly ships alone. You'll need to source exhaust gaskets and any mounting hardware separately based on your specific engine block and manifold flange type.