The models are backward compatible, so even if a model is compiled for Orangebox, it will still display properly in the EP1 engine. While the model will work to an extent, you have to make sure that
A. The model is setup on the default Valve Biped skeleton and is able to be animated
B. The model is compiled to include the CSS animations.
I suggest to you, to download Cannonfodder’s mdldecompiler and decompile the model. Once that’s done, open the .QC file with notepad and check the line called “$includemodel”
Replace the current line (if it isn’t what follows) with this:
Once you’ve done that, copy the QC file into your:
Then drag the QC onto your studiomdl.exe
With any luck, it will compile properly, and by default it will compile into your episode 2 folder.
If you have any more questions, consult the Valve wiki. It has all the information you need incase I’m being a bit too vague with my directions.