[lg's67coupe]

is it just a nut or a bolt,i think its just a stud welded to the torque converter. if so use what most people call a nut buster,or cutter. its a tool that slips over the nut
like a wrench and as you turn the opposite end of it with wrench or socket, it drives
a blade into the nut. keep turning it till cuts all the way through the nut dont go too far and damage the threads.that is if you mean that the hex head of the nut is rounded