"Burning" them out implies you need to set them on fire and produce all kinds of acrid smoke and ash. That's not the case. All you do is heat up the shell with a propane torch. Do it as evenly as possible. When the rubber bushing material starts to bubble from the heat, get some vice grips on the end of the crush tube and twist and pull. If done correctly, the rubber material will almost "pop" out and leave very little residue to clean up before sliding your new poly bushings in.

Without the proper tool, removal of the bushing is nearly impossible without damaging something...

Dale