All you need is OpenIV or SparkIV

OpenIV: https://openiv.com/
SparkIV: https://www.gtainside.com/en/gta4/tools/28310-sparkiv-0-6-6-iv-eflc/

installation:

Run OpenIV or SparkIV and go to: GTAIV\pc\models\cdimages\vehicles.img (Make sure edit mode is on) Drag the files in directory of vehicles.img (That's it!)

