Do I need a tune if I delete the catalytic converters and rear O2 sensors?

For a code-free engine, yes.

• The engine runs without cats and rear O2 sensors, but Speedway notes that missing emissions equipment may need PCM programming so it doesn't set trouble codes.
• Swap harnesses built for standalone use often leave the rear (post-cat) O2 sensors out altogether.
• If the change also affects airflow (headers, exhaust), the fuel and timing are worth retuning at the same time.

Removing cats on a street vehicle is an emissions issue in most places — check your local rules. See the swap tune checklist.

Want to do it yourself? See who tunes it, and how to learn.