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.

Well, if MachoMan has two DOCUMENTED, that settles that.

My 72 3/4 ton 400 4/spd had a steel crank.Bought a factory 4 spd,truck 440 short block from the dealer in the 80's had steel crank,six pack rods with low comp pistons.Apparently they used the rods up in the 4 spd 440 cars and trucks to the mid seventies. I have a 78 440 crate short block sitting on the engine stand right now,LY rods,cast crank and no pilot bushing machining.

Just about anything was possible.