Headers on V8 conversion
The headers you have are the typical one size fits all header everyone makes and everyone makes them slightly different and often quality control is not there.
In order to clearance headers in the past, a basic baby sledge was employed.
For use on ceramic coated headers, use the hammer to strike a towel wraped (Small pipe, wood block, etc....) item as to not make major marks and chip, gauge the coating.
This may help keep the coating in good shape, but theres no guarantee that it will come out nice, but for surely, I can guarentee it will look like heck without any protection.