Can you get it to turn at all or does it just flex the bushing until your arms give out, or is the sleeve spinning in the rubber. I had the same problem on an A-Body, they were stuck hard. The best way to break them free IMO is to drive them out. Once it starts to move it breaks free. If the head comes out much then you can clamp vice grips under the head and use drive a pickle fork between the grips and the frame to haul the bolt out, add another vice grip and use the pickle fork again. I had to use four sets of vice grips and smash two pickle forks in there to pull my bolts. Took an hour per bolt. Once you start cutting there is no turning back (although I gave some serious thought).