Add the sbuffalo folder to the dlcpacks folder (\GTAV\mods\update\x64\dlcpacks).

Open dlclist.xml (\GTAV\mods\update\update.rpf\common\data\dlclist.xml) and add the following after the last entry:

	<Item>dlcpacks:/sbuffalo/</Item>

The model spawn name is SBUFFALO.