340 Steel Crank Questions

In the late '60's, early '70's, Chrysler had a marine division that made outboards and stern drives. I know for a fact that the 150 HP stern drive was a /6 and the 250 HP was a 318. So yeah, there was a 3.31" "boat crank" per se. Can't tell much from the pics you posted in the sale listing, but the D1 78 stamping is interesting. What were the circumstances of your acquisition of the crank? If this crank was produced in 1978 it could be a marine replacement or a heavy duty truck crank. Yes it can be machined to accept a flywheel and the flange holes tapped, but it would be cheaper to buy another crank. On the other hand, are you sure the buyer is telling you the truth?

Not all marine engines are reverse rotation. The difference is the cam and water pump. Everything else is the same.