Hello, my N/A YB cosworth engine blow out number three plug, the plugs have reducer bushes in the head so the plugs are 10mm not the 13mm, the plug came out with reducer attached.

Now is it posible to to helicoil or timesert the sparkplug hole without removing the head?? if so have you any suggestions how to catch the swarf? would like to do in situ or would i just be better off removing the head. any advice would be great thanks