So to install these is pretty easy but Ill give you a little guide so you know what ur doing.
Step 1: Download the OCRP vehicles linked here.
Link: https://forum.cfx.re/t/ocrps-leo-vehicle-pack-with-templates/750695
Step 2: Go into the files and find the file called "lspdcars" then open it
Step 3: Make sure you have OpenIV installed and working with a mods folder
Step 4: Go into the "lspdcars" folder and then into each sub folder
Step 5: In each subfolder you will find 3 files look for the .ytd file and drag it into OpenIV
Step 6: Go into OpenIV and open the .ytd file and search for sign
Step 7: Replace the first file that pops up with the livies you got from me in each sub folder.
Step 8: Replace the old.ytd with the new one
Step 9: Drag into ur server files and add to server.cfg
Step 10: Enjoy ur vehicles!