If needed wherever possible locate bushing/mount point within the body and drill an aprox 1/8" hole above it to allow getting some penetrating spray on top of the bolt area.
If all the above fail to work a 3 sided cut in the floor at the mount area will also allow you to fold/peal back the metal to access the cage/bolt. Then once corrected the floor can be welded back down.
BP Buster is your friend!
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When I die, I want to go peacefully like my grandfather did, in his sleep.
Not screaming like the passengers in his car.
