Had a 78 Ramcharger w/factory 400/4spd and it was a steel crank engine..parted out a 78 W300 dually and it was a 400/4spd w/steel crank.
Out of the roughly 50+ 74-78 D&W series trucks I've owned not to mention the 100's I've seen, I've never seen a factory cast crank BB 4spd truck or a factory 440 4spd truck.
But as many have said I've learned to "never say never" with ma Mopar.