Open the .oiv with winrar.
Put all vehicle files in the vehicle.rpf of the newest patchday.
Add the content of the vehicle.meta from .oiv to the vehicle.meta in the newest patchday. Same with carols and carvariantions.meta.
Add the content also to the same files in mods/update/update.rpf.
If you don't find the files. Search in openiv after the files.
I got it to work with the newest version.
I opened the .oiv with winrar an installed the mod like a normal addon, added the carvariation.meta to the existing one. Same with the carols and vehicle.meta it all worked. :)