i got a 78 20r with a broken header bolt. if it was on the middle of the header where the other one would hold it down it would be no bilg deal. but its on the end close to the firewall. does anyone know how to do this. i have never done this before. thanks ahead of time

break off even with the head?
penetrating oil is your friend. if its even with the manifold, if you feel like taking it off, visegrip it. i think it would be hard to get a drill in there.

its broken off even with the motor. but is the bolt threaded into the motor?

EZout bit.

your going to have to drill it out and EZ-out the stud. i had the same exact thing happen to me on my 22r. same spot and everything. mine was the one in the far back on the bottom. if you have a drill small enough to get in there use a drill and easy out the stud, my threads stripped out so i had to use a heilie coil. however, as long as your threads are still good when the stud comes out, you'll be fine. the drills i had were all to big and hit the brake booster. i ended up buying an adaptor that goes on the end of the drill which turns the drill head 90 degrees. you can find them at home depo. it allowed me to stand in front of the truck holding the drill parallel with frame and drill to my left. worked perfect. just be careful when drilling, you want to keep the threads intact.... a heilie coil kit is expensive. i think mine was like 90 bucks or so. good luck! and like kdc said penetrating oil will also help get through the hardened steel.