These motors are known for that problem. Or blowing the plug centers out leaving the threads siezed to the head.
Yes they can be heli coiled on the vehicle. Not the best thing. But, I used to do it on the local power companies vans. They wouldn't pay to have it done off the vehicle. I made a tool to get the plug threads out. Doing the heli on a 5.4 in a van is a real adventure.