External or Internal Flywheel… need asst.

Why is the flywheel "spent"? As said, that is a neutral balanced flywheel which would seem to indicate a steel crank, but that's no guarantee. Can you get us a picture of the balancer? If it's also a neutral balancer, then chances are it's a steel crank. Did the engine run smoothly with no vibrations? The only real way to make the determination between steel or cast is to get the oil pan off.