Your dilemma sounds like some I have had working on motorcycles and the phillip's head screws. Best thing I ever did years ago was by a hand held impact driver that was activated by a blow of a hammer. That is what I would try first. Good luck and I am sure there will be others who have had similar difficulties of bolt/screw removal.

After re-reading your question, it looks like the access to the bolts may be restricted. With that in mind, how about a ratchet with an hex head adapter for the screws. Mine have allen heads