I assume you've installed it by executing the otx?
It should be in the user data folder for Outerra. Default location is "c:\Users\{windows-user}\Outerra" for me ( Win 8 ).
When you install the otx, its contents are extracted into this folder.
In this case the exact location should be:
"c:\Users\{windows-user}\Outerra\packages\bugsblake\ford mustang bullet2\"
BTW: I noticed the wheel size seemed a bit off (the car hovered a bit), so I tweaked it a little. It is not entirely to my satisfaction yet, but it works. See attachment.
I hope this helps.