Drilling off the heads and driving down? Or cutting off the bent portion of the bolts from the bottom? The first one is probably the easier and for sure your body is also in a much better working position than from underneath. Having a drill bit sharpener on hand or at least several extra sharp drill bits will assist with progress.
For the from-the-bottom alternative, I have cut through many stainless steel bolts with the Dremel tool cut-off wheel attachment pictured below. The wheels come in two thicknesses. The thinner ones work the best. Also real Dremel brand wheels (or Craftsman brand) are definitely superior to the Harbor Freight no-name variety. If you haven't used these before, note that the wheels are very brittle. Unless you've got a Midas touch, and even if you do, the wheels will most often break before they wear down. When they break, pieces go flying. So eye protection is an absolute must. And if the confines of the working space force the face to be close to the action, also a full face cold weather mask will protect from some stinging. It's important also to keep face and eyes off the plane of the rotational axis.
Even if you don't use the Dremel for this project, I decided to post this info because my Dremel and the various attachments are incredibly useful on my boat. Often the solution that nothing else can substitute for. If you don't have a Dremel, I've seen adds for Dremel knock-offs at Harbor Freight for under $10 -- with a selection of accessories. These will definitely be inferior to the real Dremel or Craftsmen brands, but doesn't cost much to experiment to see if also useful for you. I've got AC powered Dremels/Craftsman. I don't know about the battery powered ones.
