Yes, I have the headers loose down at the collector. I also used an open wrench to get the bolt to this condition. It was just as you described a series of small rotations with the open wrench, but the bolt head ultimately contacts the piping. I started to tighten the bolt back up to gain space and I was going to get the file out to make some room. I don't plan to reuse the headers, but did not want to destroy in case somebody wanted them.

The front bolt issue seems to be a better condition then the rear (see new photo).