I have a 1977 300-D. I'm tring to replace my door striker, but I can't get the bolts out. They are so tight, I'm worried about stripping the bolt heads. I've tried loosening them with PB Blaster to no avail. Anybody have any experience with this?

 

I tried using the impact tool, finally drilled the head off and I was able to remove the remaining stud on my striker.