Get a hammer and good sized punch and whack the top of each bolt. sometimes you get lucky and this breaks them loose. when that doesn't work, get a big, air powered impact and give them hell until the heads round off. An impact socket w/ no extension transfers the most shock. Drill or chisel the bolts heads off and pull the head. Try and take the studs out with a vise grip. When they twist off, grind them flat and drill through whats left. You can try eazyouts, snap-on makes the best, but they wouln't help. Once you drill out the body of the stud, try and peel the thread out of the hole. If that does't work drill tap and Helicoil. If you drill into the water jacket, coat the helicoil in JB weld before you install it to seal the water jacket.
As I said before, your F**ked