how tight is your space around the bolts? do you have an air compressor? I have used all the following to remove bolts that are rusted too badly: plasma cutter (interesting, works fast but you have to be careful), angle grinder with cutoff wheel (takes the most space), die grinder with cutoff wheel (less space than the angle grinder), and an air chisel. the air chisel gets the most use, it works great. shear off the head of the bolt then punch out the remaining portion.

If you are tight on space, budget and equipment get yourself a dremel with a cutoff wheel, it will take longer but hey, in a pinch you make do right.

Red