RW&A Budd RDCs
This pack contains two variants of Budd's RDC, the RDC-2 and RDC-3, in the Riverside, Waterton, & Atlantic scheme. These are intended to run on the RW&A donationware route from Railworks America, but they can of course be used anywhere.
Michael Stephan's Alaska Railroad RDCs, which can be found here
To install these, just drag and drop the "Assets" folder included with this download into your main RailWorks folder, and if asked to merge folders say yes. That should be it. Because the original model is freeware, all the shape files are included; the original set of RDCs is still required for sounds and other shared components.
To use these in a scenario, the "VNHRR\BuddRDC" box must be ticked. They will then show up in game as "Budd RDC-2/3 RWA..."