Stimpy---To save the locating dowel position, and save the block without taking it to a machine shop, you may have to make a drill jig out of 3/4" or 1" plate, with a shape and bolt pattern that exactly matches the waterpump housing. Use a set of transfer punches to exactly duplicate the positions of the water pump bolts and the dowel pin, but don't drill the holes oversize---drill them about .005 thou. greater than the actual water pump bolts and dowel.---On the position that has the broken stud, drill that hole the same diameter as the tap drill for whatever sized bolt you are removing. Bolt the plate onto the block, and use it as a guide to drill out the broken bolt. That way, your drill will not "wander" and the position will be dead nuts. If the threads are totally stripped out, you can use the same method to accurately position a helicoil----Or---drill and tap one size larger and use a "stepped" stud, on which the threads on one end screw into the block, while the smaller threads on the other end match your waterpump bolts.