One thing to keep in mind is that the N&W was the last class I to fully dieselize and by the time they did, the cab unit era was mostly a thing of the past. It is really a testament to their mechanical department on how well their steam fleet was maintained.
As others have mentioned, the few cab units came with the Wabash merger. CNJ leased some in the early 1970's. They went as far as to repaint one into CNJ colors, but when the N&W found out CNJ had to repaint it back. 
Even if they were a bit utilitarian in looks, those Redbird GP9s were classy looking passenger locomotives.
