If you do round off the head I found this Gator Grip socket works. You can get them at Sears among other places.


Gator grip from Sears

 

Don't forget heat, I find cleaning the exposed threads with a dremel tool and then heating the bolt for a few seconds with a MAPP torch really helps those stubborn ones.

 

I used the angle grinder with a thin wheel where reachable and the tighten till they break on the ones at the top. Not one of mine on either side actually unscrewed. Good luck with yours, not a fun chore when the truck is together.