I believe it is, but wanted another opinion.

Ok guys take a look at this crank. I'm a bit of a newb but i'm learnin. Now from what I've read a factory steel crank has a casting line of aproximate 1/4" vs the pencil sized line of the cast. Also the steel has a rounded more uglier casting than the factory cast. I've also read that in a 400 B block '72-'73 was the last year they used the steel crank. Is this correct? The reason I ask is because I recently bought a '76 casted 400 engine, when I started tearing into it I found this beautiful piece. So can anyone enlighten me on this, is this a true steel crank? If so how'd it end up in a '76 engine?