On the one that is sticking out the 1/4 inch, lay a flat washer over it, slide a nut over the broken stud. Weld the nut to the stud. Let it cool. If you soak it good first might help too. Have you heard of the bees wax trick? We used it a lot to get oil gallery plugs out and I worked on an Old A John Deere. It worked good although I had to to a few of them twice. Heat the stud(aim the torch sideways) till it is a dull red. Place the bees wax on it. It will smoke and then the wax melts and runs down the thread. Let it cool turn it with a pipe wrench. If it does not turn try it again. Also for new head studs I use Continental head  studs. They are about 1/4 inch longer, have the washer right on them. Easy to find, also if you loose the valve keepers the continental ones are or were available from NAPA (I have part number if you need it). They are about a 16th too long just grind it off. Tap all the head bolt holes in the block and put teflon paste on the threads. Questions or want to talk send me a P M.