heh the "coil" you refer to in the threads of the short end of the stud is actually aluminum from your head. those were the threads in the head that held the stud in place. because they are old and soft, when you tried to torque the nut, you spun the stud and ripped the threads right off. now you have a nice smoothish hole in your head that you can't properly thread a stud into. you will need to drill out the holes in the head and then helicoil them.
pretty sure this has already come up in this thread, but ill mention it again: driftmotion has an excellent kit for this project. you get the drill bit, the tap, the studs, the nuts, and the heli coil inserts all for $70 bucks. and it comes with a tap handle, cutting oil, and i think it also comes with the insert tool for the heli coils. as someone who used it, i fully endorse the product.