Are you sure it is steel? No matter what anyone told me if I see a casting with a crack I immediately suspect it is cast iron. The welding technique is different for the two materials and I have never had success with stick welding cast iron but steel is a different matter. I would use stick 7018 and would preheat the casting to several hundred degrees before welding. Probably also vee the crack to get penetration and drill a small hole through at the tip of the crack to help ensure it did not propagate further.
The main problem in welding castings is shrinkage cracks adjacent to the weld and changes in the metal properties in the heat affected zone. You probably do not know the steel composition but when it is a casting it is likely that it is a medium carbon steel, maybe even an alloy steel, so a concern is making it brittle in the heat affected zone.
Realistically you do not have anything to lose because the casting is no use with the crack. Wait and see what other suggestions are posted and then make your decision.