Yea either 1) Call BAMA and figure things out that way or 2) Put cats back on and take it back to Ford
Either way if you're running O2 sensor extensions I would take them off
Does it only clunk over uneven ground? What happens if you go over a speed bump? Does it only happen when you shift or accelerate? Describe the situation a bit more
1. Check your oil every day during the first few thousand miles, once a week afterwards at least.
2. Run an oil catch can
3. Keep an eye on your coolant levels and temp guage.