To install with OpenIV you replace the provided 
vehicle files here:
 
GtaV\mods\update\x64\dlcpacks\mpstunt\dlc.rpf\x64\levels\gta5\vehicles\mpstuntvehicles.rpf
GtaV\mods\update\x64\dlcpacks\patchday12ng\dlc.rpf\x64\levels\gta5\vehicles.rpf

And the meta files go in these places:
 
GtaV\mods\update\x64\dlcpacks\mpstunt\dlc.rpf\common\data\handling.meta
GtaV\mods\update\x64\dlcpacks\mpstunt\dlc.rpf\common\data\levels\gta5\vehicles.meta
GtaV\mods\update\update.rpf\dlc_patch\mpstunt\common\data\levels\gta5\vehicles.meta


 Thanks for downloading.