Removing Bumper

69B-Cuda said

spray the heck out of them with some penetrating oil for a couple days....If they are real rusty, when you take them off, as you loosen them up, loosen them maybe 1/2 -3/4 turn then tighten again and go back and forth, loosen and tightening them and spraying with more penetrating oil and gradually working them off. This seems to work well and keeps them from breaking and/or stripping.

Click to expand...

x2 PB Blaster works very well for this.
After you spray the bolts the first time, use a hammer to tap lightly on the nuts and bolts. That sometimes cracks the rusted bond enough to allow the oil to seep into the threads.
If they don't loosen after a couple of days soaking, try the procedure again with a little more force with the hammer.
I've had to do repeat soakings/tappings several times with head bolts and exhaust manifold bolts. Haven't broken one off yet.

The main thing is to be patient and let the oil and tapping do their job.