As Rusty said, soak both sides with Kroil, PB Blaster, WD40 or your preferred penetrating oil. Let set a day or two and do it again. Let set another day and spray both sides again then tap the heads a few medium strokes of the hammer. Then try to just tighten (not loosen) a bit. Then spray again and see if they will come out. Good luck.

Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!
USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)