Looking at pictures of BNs (4081-4086) ex NP 1955 RS-3 order (857-862 made it to BN), it looks like all were built as or modified while still NP units to operate short hood forward. I think that it would be rather expensive to convert a unit after it was built, so the railroad would have to have a good reason to do so. A picture of Alco RSD-5 Demonstrator 1606, which became ATSF 2157, shows that it was built as short hood forward.
I have a friend who was a B&M Connecticut River engineer. That line got most of the older power. He says that he hated the Alcos because of being long hood lead. At the same time, the contemporary EMD units were all ordered short hood lead. Who knows why the company would order one specification from one builder, and the opposite from the other.
Maybe EMD had short hood front standard, while Alco's standard was long hood. It may have been an extra cost option, which some companies may not have been willing to spend on.