You need to add the .dat files (models) inside the Raw folder of your cache. Your cache should be in C:/.
After that, you go in your ItemDef class (or ItemDef_2 if your client uses it) and you just need to copy one of those if statements (or case) and paste it.
Make sure to change the modelID to the number of the model you put in the Raw folder of your cache. Change the name, description, etc.
I suck at explaining, so, check this out
Good luck!