Do I need to upgrade my exhaust downpipe to fit this manifold?

Your downpipe must accept a T3 flange outlet to bolt directly. If your current downpipe uses a different flange type, you'll either need a new downpipe or an adapter — check your turbo kit specs before ordering.

Are factory K20 mounting bolts required, or do I need to source new hardware?

Factory K-series block bolts work at the manifold mounting points. Bring your existing hardware to a test fit first — if threads are stripped or bolts damaged, you'll need replacements, but the manifold itself doesn't ship with fasteners.

Should I use a manifold gasket between this and the engine head?

Yes. A quality exhaust manifold gasket rated for K-series engines prevents boost leak and prolongs seal life. This manifold ships bare — grab a gasket kit when you order.