Sorry, I should've been more clarified.
It's a custom model that I downloaded off a website, are the steps basically the same? I don't really understand the "the models folder from the GFCScape file" part.
I also have another question: Let's say you wanted to modify an existing default model (a DoD: S model in my case), where exactly would you find the file for the model? I can view the default DoD models with Half Life Model Viewer but I can't seem to find the actual thing, isn't it in the .gfc file?