Add-On Method: 
-Open your GTA5 Main Directory
-mods, update, x64, dlcpacks, then drop the "rx450" folder from this archive
-Then, open OpenIV.
-mods, update, update.rpf, common, data, drag and drop "dlclist.xml" to your desktop.
-Open with Notepad.
-Scroll to the end of your dlc list and paste this: 	
		<Item>dlcpacks:\rx450\</Item>
-Hit save, then replace in OpenIV.	
-Spawn in game using " rx450 "