rear body mount bolt HELP!!

[i heart square bodys]

hey guys ive been messing around with this for ages and came to seek help from someone that has experienced this. i had to cut the head off the bolt to remove my cab , the bolt just spins freely and will not loosen, it is the rear passenger bolt. i noticed on the other side that the nut inside floats and is not welded to the inside of the crossmember. what is the best way to fix this !? strange thing is that the bolt is a fraction of a fraction of an inch from comming out ! HELP!