I would try to crank the engine over before I do anything. The manifold
probably cracked due to the water in it freezing (Did someone winterize
the engine and exhaust system?), when that water thaws out it
frequently runs down into the exhaust port, and into the head/cylinder.
At that point your looking at a much bigger problem, so cross your
fingers and crank the engine over to make sure it spins. If it does,
you should be OK. But pull the dip stick as well, to make sure the oil
level isn't way up, indicating water in the oil.