Step 1: Start OpenIV and open x64e.rpf in Edit mode.
Step 2: Browse to levels -> gta5 and extract vehicles.rpf to somewhere within the GTA 5 main folder.
Step 3: Delete vehicles.rpf from x64e.rpf and rebuild the archive.
Step 4: Open the extracted vehicles.rpf archive.
Step 5: Drag all the included .ytd files into the archive, this will replace the existing files.
Step 6: Do not rebuild vehicles.rpf, open x64e.rpf instead and browse back to levels -> gta5.
Step 7: Drag the modified vehicles.rpf back into the gta5 folder within x64e.rpf.
Step 8: Do not rebuild x64e.rpf, simply close OpenIV.