We raced rally raced a rental in h/s. Friends older brother rented it, ripped out the rear seat, welded in a roll bar and raced it. Cleaned it up, cut out the roll bar, put the seats back in it, made a lower bumper valence piece out of some large white PVC to replace the one that got ripped off and returned it.
I'm assuming you know about the Shelby Hertz rental mustangs back in the day and the stories behind those...
Friend of mine used to work for boyd cottington. They rented a ferrari for a month, pulled the whole drivetrain out and built a 30's ford based around it. Then put the drivetrain back in the ferrari and returned it. Ferrari took longer then anticipated to deliver so it worked as plan b. That same guy now works for Chip Foose as his main chassis guy.