2000 Chevy Blazer head gasket replacement vs. cracked head

What is the surest way to tell if you have only a head gasket replacement problem instead of a cracked head without taking the engine apart?

I have a car that I want to sell after repair . I have all the symtoms of blown head gasket with white smoke out of tailpipe, missing engine and in fact, a crack and leak in the radiator. However, If head is cracked and requires replacement or new motor, I may sell as is. If it is a head gasket only, I am willing to make investment.