Installation:
Once downloaded, unzip to anywhere you want.
Now, in OpenIV, go to "mods/update/x64/dlcpacks/", drag and drop folder called "ProjectCalifornia" from archive here
Go back to "mods/update/". Now, go to "update.rpf/common/data/" and click edit on "dlclist.xml".
Add new line: dlcpacks:\ProjectCalifornia\
Save.

Enjoy!