Addon:

First, go to gta5 / mods / update / x64 / dlcpacks

Make a new folder, title it "mach1", and drag dlc.rpf into the folder.

Then, go to gta5 / mods / update / update.rpf / common / data

Edit dlclist.xml, add "<item>dlcpacks:\mach1\</item>"  above "</Paths>"

Make sure to save.

To spawn the car ingame, use a trainer to spawn by spawn name and type "mach1"

To make sure your game doesn't crash, download and install a custom gameconfig such as:
https://www.gta5-mods.com/misc/gta-5-gameconfig-300-cars

If you use tkownz Dynamic Indicators script, add this to the bottom of tk0wnz-indicators.ini, without the ".
"ModelName4 = mach1
 Duration4 = 750"




