The old manifold will be warped so when repairing this concern be sure to install a new manifold kit as shown Here- (check fitment guide)
https://www.amazon.com/gp/product/B00GHT7ZFG/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B00GHT7ZFG&linkCode=as2&tag=fordt-20&linkId=4EA36YKW5X2TAU2A
Most important is to replace the manifold studs and nuts with a stainless steel kit-
https://www.amazon.com/gp/product/B00W98JV42/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B00W98JV42&linkCode=as2&tag=fordt-20&linkId=OKBJOZSLLA7QNCYH
Don’t forget Nickel Anti-Seize for the down pipe studs-
https://www.amazon.com/gp/product/B000NUBH22/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B000NUBH22&linkCode=as2&tag=fordt-20&linkId=XIVZ2TAV6NJSLWUQ
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A simplified overview of Oxygen Sensor diagnosis and replacement. This is a simple approach and brief overview.