Does this header work with a stock downpipe?

Yes, the collector design is compatible with factory and most aftermarket downpipes. Confirm your downpipe flange matches before purchase.

Will this header need a tune or O2 sensor relocation?

Header installation typically doesn't require engine tuning or sensor work if you're keeping your stock emissions setup. If running a full exhaust system, refer to your system manufacturer's instructions.

What prep is needed before installation?

Remove the factory header and clean the head mating surface. Apply a gasket sealer designed for header applications before bolting down. Torque specs are in your vehicle service manual.