Don't confuse WD-40 or Liquid Wrench with PB Blaster. That stuff
works like nothing I have ever seen.

I'll second that. PB beats the others.

One other approach you might want to take, is to turn the engine on
it's side, put a wrench on the bolt and rig a 20 pound weight on one
end being very liberal with the PB Blaster.

Tap on the head of the bolt a few times with a hammer, apply the PB, rig up
the wrench/weight and wait a few hours. Repeat.

Give it about twelve hours and it will come free.

Yep, got some seriously frozen brake caliper bolts loose this way.

Otherwise, if you can remove the item with the bolt shaft still in the block
then drill or grind off the head of the bolt. That's assuming torque
doesn't snap it off anyway.