since the end studs go into the water jacket, it is a lot cleaner to keep them as studs. If you use bolts, whenever you pull them out, you will get a puddle of water dripping out onto the floor.
What he said and it will be a huge puddle. I use permatex high temp RTV sealer on those threads. The one that comes in the bronze tube. Any good auto parts store will have it. Wipe hole and stud down with Brake Parts Cleaner to remove all oils before hand and you won't be leaking...