Been there had that happen, usually when I try to remove the bolts w/o loosening them fairly evenly.
Sorry James..I should have remembered and warned you about that bracket. Take the bolt out of the tb and pry that bracket forward..it'll move out of the way.
That broken bolt you have a couple choices..one is drill and tap, If you can get a hold on it..it should move forward as if you were screwing it in..which would remove it in your case. Another is to use a air hammer or air chisel and punch it through. Then put a bolt with nut on there to hold the exhaust when you put it back together.
00 Regal GS: All kinds of cool stuff.