John,
I have never had an issue with the older Kato SD40-2 locos and DCC, the Digitrax DN163K1B is designed to fit them. I have a couple of NS examples from the same era and installation was as easy as it comes.
Since Kato started to re-release all their existing models in various hues of BNSF colours they have taken the previous listings of old, out of production models off the website. I would recommend getting a copy of the Kato Parts Catalogue from their Parts store,(if you can get one) has a full? listing of their old models and the parts that correspond.
Hope that helps
Alasdair