Do these headers require new exhaust piping downstream?

Depends on your current exhaust setup. If you're running stock manifolds with an intact system, test-fit the header outlet diameter against your existing pipe before ordering new exhaust work.

What do I need to know about installation?

Mounting points and hardware requirements aren't specified — verify fitment at the engine bay and exhaust ports before committing. You may need gaskets, fasteners, or adapters depending on your truck's current configuration.

Will these need painting or any prep before installation?

Stainless steel doesn't rust, so no paint is necessary. You can install straight out of the box, though some builders choose ceramic coating for heat management — that's optional based on your preference.