Installation: 

1: Extract the contents of the folders to the .rpf achives in "C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\update\x64\dlcpacks\mpgunrunning\dlc.rpf\x64\levels\mpgunrunning\vehiclemods" with the same names as the folders.
N.B. Use Edit Mode in OpenIV

Also, Ardent livery goes here:
C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\update\x64\dlcpacks\patchday19ng\dlc.rpf\x64\levels\patchday19ng\vehiclemods\ardent_mods.rpf\