With the advent of Immersive Railroading 1.0, a few of the older style models have been retired. If you still wish to use them, I have uploaded this resource pack.
This resource pack re-adds the following models:
* GP-7 Diesel locomotive
* Original Freight Car
* Original Tank Car
* Original Flatbed Car
Client side install it as a normal resource pack
Server side drop it in the config/immersiverailroading folder