Hi there, I'm Snake. If you wanna install the mod you have to open SparkIV (Or OpenIV) 
and there you click "Open" and search your GTA IV Directory, example:

D:\SteamLibrary\steamapps\common\Grand Theft Auto IV\GTAIV

When you're there, you have to open; pc/models/cdimages/weapons

Open weapons and then, import the file there, click save and ready. You'll have the mod. 
