Its very doubtful you'll shear the tower bolt, its thick steel and pretty strong. You could try squirting a bit of penetrant down between the bulkhead and subframe towers, its possible some would get down inside the threads.
My advice would be to extend your breaker bar, I needed an 18" long one to get mine undone. You already seem aware of the possibility of damaging your tools, so be careful of cracking the outer wall of the socket, particularly if it is of the 'multi-hex' design. If possible try to get hold of an impact socket, these have a hexagonal design, and much thicker walls, so the possibility of cracking is much less. Similarly the chances of slipping is reduced, so rounding off the head of the bolt isn't so much of an issue.
Also, for reference, try to avoid using a ratchet to undo tight nuts/bolts (I know Minilady isn't, but some people do!). A ratchet is a convenience tool, designed to speed up the removal of nuts, not as a tool to take serious abuse. Inside the head of the ratchet are small pawls and ring gear, and big forces through there can sometimes result in them breaking, usually rather violently - with the result of your knuckles/elbow/head/shoulder/whatever suddenly accelerating towards the nearest solid object - usually something sharp and steel - which is pretty painful!! So when undoing tight fittings, try to use a breaker bar with a tubular extension if necessary, its much safer, and means your ratchet lasts much longer!
) to apply twisting forces.
