40 water pump bolt head broke off what now?

[L78CHEVELLE]

Water pump was leaking on a 72 year old engine. All the bolts came out except the two inside the water intake hole of the pump. The heads stripped off. I took the pumps off and there is about 1/2 inch sticking out on one side and about 1/4 inch on the other side. Can you heat the block and turn these out with Vise Grips? What methods have you used to correct this problem?