The way I have handled that in the past is to remove the spark plug and then put just the spark plug socket back close to the position it is in to remove the spark plug, but touching the header, and use a hammer to beat on the top side of the spark plug socket. It will leave a perfect indention in the header to clearance the plug wire. It will be a trial and error thing, just make sure to take your time and clearance a little at time and recheck. No sense in making a bigger dent in the header pipe than necessary. I don't know if you will get a quarter inch clearance, but it should never be touching. After you are done, pull the headers off and clean and paint. I would personally not use header wrap.